PENSIONS AND OTHER POSTRETIREMENT BENEFITS (Benefit Obligations, Fair Value of Plan Assets, and Net Funded Status) (Details) - USD ($)
$ in Millions |
12 Months Ended |
|
|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2016 |
Dec. 31, 2015 |
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
$ 193.4
|
$ 188.1
|
|
|
|
| Employer contributions |
1.1
|
3.5
|
|
|
|
| Fair value of plan assets — end of year |
202.4
|
193.4
|
$ 188.1
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
193.4
|
188.1
|
188.1
|
$ 202.4
|
$ 193.4
|
| Amounts recognized in Statements of Financial Position: |
|
|
|
|
|
| Assets, Current |
|
|
|
824.6
|
982.7
|
| Noncurrent liabilities |
|
|
|
(280.5)
|
(221.0)
|
| Pension Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(910.8)
|
(998.0)
|
|
|
|
| Service cost (excluding expenses) |
17.6
|
22.7
|
26.1
|
|
|
| Interest cost |
30.3
|
37.7
|
40.3
|
|
|
| Plan amendments |
5.7
|
0.0
|
|
|
|
| Actuarial loss |
(21.1)
|
(20.8)
|
(14.0)
|
|
|
| Defined Benefit Plan, Change in Actuarial (gain) loss |
38.1
|
(67.7)
|
|
|
|
| Benefits paid |
(70.9)
|
(78.7)
|
|
|
|
| Participant contributions |
0.0
|
0.0
|
|
|
|
| Federal subsidy on benefits paid |
0.0
|
0.0
|
|
|
|
| Benefit obligations — end of year |
(931.6)
|
(910.8)
|
(998.0)
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
700.6
|
749.8
|
|
|
|
| Actual return on plan assets |
54.8
|
(6.4)
|
59.1
|
|
|
| Participant contributions |
0.0
|
0.0
|
|
|
|
| Employer contributions |
1.2
|
35.7
|
|
|
|
| Assets Transferred to (from) Plan |
0.1
|
0.2
|
|
|
|
| Fair value of plan assets — end of year |
685.8
|
700.6
|
749.8
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
700.6
|
749.8
|
749.8
|
685.8
|
700.6
|
| Defined Benefit Plan, Benefit Obligation |
(910.8)
|
(998.0)
|
(998.0)
|
(931.6)
|
(910.8)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
(245.8)
|
(210.2)
|
| Total amount recognized |
|
|
|
(245.8)
|
(210.2)
|
| Amounts recognized in Statements of Financial Position: |
|
|
|
|
|
| Assets, Current |
|
|
|
0.0
|
0.0
|
| Current liabilities |
|
|
|
(0.1)
|
(0.5)
|
| Noncurrent liabilities |
|
|
|
(245.7)
|
(209.7)
|
| Total amount recognized |
|
|
|
(245.8)
|
(210.2)
|
| Amounts recognized in accumulated other comprehensive income: |
|
|
|
|
|
| Prior service cost |
|
|
|
11.0
|
7.5
|
| Net actuarial loss |
|
|
|
315.9
|
290.9
|
| Net amount recognized |
|
|
|
326.9
|
298.4
|
| The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost: |
|
|
|
|
|
| Net actuarial loss |
21.1
|
|
|
|
|
| Prior service cost |
2.6
|
|
|
|
|
| Net amount recognized |
23.7
|
|
|
|
|
| Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments |
0.0
|
(1.2)
|
|
|
|
| Other Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(266.0)
|
(295.8)
|
|
|
|
| Service cost (excluding expenses) |
1.7
|
6.4
|
1.8
|
|
|
| Interest cost |
9.1
|
13.4
|
11.9
|
|
|
| Plan amendments |
9.8
|
0.0
|
|
|
|
| Actuarial loss |
(6.0)
|
(6.6)
|
(4.5)
|
|
|
| Defined Benefit Plan, Change in Actuarial (gain) loss |
(7.2)
|
(27.0)
|
|
|
|
| Benefits paid |
(21.3)
|
(20.6)
|
|
|
|
| Participant contributions |
6.0
|
4.0
|
|
|
|
| Federal subsidy on benefits paid |
0.5
|
0.4
|
|
|
|
| Benefit obligations — end of year |
(264.6)
|
(266.0)
|
(295.8)
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
250.6
|
269.3
|
|
|
|
| Actual return on plan assets |
16.0
|
(3.9)
|
31.9
|
|
|
| Participant contributions |
0.5
|
0.4
|
|
|
|
| Employer contributions |
1.7
|
1.3
|
|
|
|
| Assets Transferred to (from) Plan |
0.0
|
0.0
|
|
|
|
| Benefits paid |
(15.8)
|
(16.5)
|
|
|
|
| Fair value of plan assets — end of year |
253.0
|
250.6
|
269.3
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
250.6
|
269.3
|
269.3
|
253.0
|
250.6
|
| Defined Benefit Plan, Benefit Obligation |
(266.0)
|
(295.8)
|
$ (295.8)
|
(264.6)
|
(266.0)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
(11.6)
|
(15.4)
|
| Total amount recognized |
|
|
|
(11.6)
|
(15.4)
|
| Amounts recognized in Statements of Financial Position: |
|
|
|
|
|
| Assets, Current |
|
|
|
|
0.0
|
| Assets, Noncurrent |
|
|
|
27.3
|
|
| Current liabilities |
|
|
|
(4.1)
|
(4.1)
|
| Noncurrent liabilities |
|
|
|
(34.8)
|
(11.3)
|
| Total amount recognized |
|
|
|
(11.6)
|
(15.4)
|
| Amounts recognized in accumulated other comprehensive income: |
|
|
|
|
|
| Prior service cost |
|
|
|
(26.9)
|
(39.5)
|
| Net actuarial loss |
|
|
|
87.0
|
91.5
|
| Net amount recognized |
|
|
|
60.1
|
52.0
|
| The estimated amounts that will be amortized from accumulated other comprehensive income into net periodic benefit cost: |
|
|
|
|
|
| Net actuarial loss |
5.0
|
|
|
|
|
| Prior service cost |
(3.0)
|
|
|
|
|
| Net amount recognized |
2.0
|
|
|
|
|
| Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments |
0.0
|
0.0
|
|
|
|
| Salaried Employees [Member] | Pension Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(340.0)
|
|
|
|
|
| Benefit obligations — end of year |
(351.9)
|
(340.0)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
258.3
|
|
|
|
|
| Fair value of plan assets — end of year |
242.9
|
258.3
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
258.3
|
258.3
|
|
242.9
|
258.3
|
| Defined Benefit Plan, Benefit Obligation |
(340.0)
|
(340.0)
|
|
(351.9)
|
(340.0)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
(109.0)
|
(81.7)
|
| Salaried Employees [Member] | Other Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(38.2)
|
|
|
|
|
| Benefit obligations — end of year |
(37.6)
|
(38.2)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
0.0
|
|
|
|
|
| Fair value of plan assets — end of year |
0.0
|
0.0
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
0.0
|
0.0
|
|
0.0
|
0.0
|
| Defined Benefit Plan, Benefit Obligation |
(38.2)
|
(38.2)
|
|
(37.6)
|
(38.2)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
(37.6)
|
(38.2)
|
| Hourly Employees [Member] | Pension Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(558.6)
|
|
|
|
|
| Benefit obligations — end of year |
(565.6)
|
(558.6)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
436.7
|
|
|
|
|
| Fair value of plan assets — end of year |
436.9
|
436.7
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
436.7
|
436.7
|
|
436.9
|
436.7
|
| Defined Benefit Plan, Benefit Obligation |
(558.6)
|
(558.6)
|
|
(565.6)
|
(558.6)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
(128.7)
|
(121.9)
|
| Hourly Employees [Member] | Other Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(227.8)
|
|
|
|
|
| Benefit obligations — end of year |
(227.0)
|
(227.8)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
250.6
|
|
|
|
|
| Fair value of plan assets — end of year |
253.0
|
250.6
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
250.6
|
250.6
|
|
253.0
|
250.6
|
| Defined Benefit Plan, Benefit Obligation |
(227.8)
|
(227.8)
|
|
(227.0)
|
(227.8)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
26.0
|
22.8
|
| Mining Employees [Member] | Pension Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(8.6)
|
|
|
|
|
| Benefit obligations — end of year |
(10.0)
|
(8.6)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
5.6
|
|
|
|
|
| Fair value of plan assets — end of year |
6.0
|
5.6
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
5.6
|
5.6
|
|
6.0
|
5.6
|
| Defined Benefit Plan, Benefit Obligation |
(8.6)
|
(8.6)
|
|
(10.0)
|
(8.6)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
(4.0)
|
(3.0)
|
| Supplemental Executive Retirement Plan S E R P [Member] | Pension Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Benefit obligations — beginning of year |
(3.6)
|
|
|
|
|
| Benefit obligations — end of year |
(4.1)
|
(3.6)
|
|
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
|
|
| Fair value of plan assets — beginning of year |
0.0
|
|
|
|
|
| Fair value of plan assets — end of year |
0.0
|
0.0
|
|
|
|
| Funded status at December 31: |
|
|
|
|
|
| Defined Benefit Plan, Fair Value of Plan Assets |
0.0
|
0.0
|
|
0.0
|
0.0
|
| Defined Benefit Plan, Benefit Obligation |
(3.6)
|
(3.6)
|
|
(4.1)
|
(3.6)
|
| Defined Benefit Plan, Funded Status of Plan |
|
|
|
$ (4.1)
|
$ (3.6)
|
| Pension Costs [Member] | Pension Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Service cost (excluding expenses) |
17.6
|
22.7
|
|
|
|
| Interest cost |
30.3
|
37.7
|
|
|
|
| Pension Costs [Member] | Other Benefits [Member] |
|
|
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
|
|
| Service cost (excluding expenses) |
1.7
|
1.9
|
|
|
|
| Interest cost |
$ 9.1
|
$ 11.5
|
|
|
|