Cleveland-Cliffs Inc. Annual report pursuant to Section 13 and 15(d)

Annual report pursuant to Section 13 and 15(d)

PENSION AND OTHER POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Other Benefit Plan Assets) (Details)

PENSION AND OTHER POSTRETIREMENT BENEFITS (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Other Benefit Plan Assets) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	$ 188.6	$ 200.5
Actual return on plan assets:
Relating to assets still held at the reporting date	15.9	41.0
Acquired through business combinations	6.8	145.0
Sales	(7.0)	(172.8)
Fair value of plan assets — end of year	205.8	188.6
Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	57.6	85.6
Actual return on plan assets:
Relating to assets still held at the reporting date	3.1	4.5
Acquired through business combinations	0	66.0
Sales	0	(97.3)
Fair value of plan assets — end of year	59.2	57.6
Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	29.1	29.3
Actual return on plan assets:
Relating to assets still held at the reporting date	3.2	(2.1)
Acquired through business combinations	1.4	14.7
Sales	(5.5)	(18.0)
Fair value of plan assets — end of year	31.2	29.1
Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	40.9	29.4
Actual return on plan assets:
Relating to assets still held at the reporting date	5.2	5.1
Acquired through business combinations	5.4	36.8
Sales	(1.5)	(30.0)
Fair value of plan assets — end of year	50.0	40.9
Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year			237.0
Actual return on plan assets:
Fair value of plan assets — end of year	269.3	251.8	237.0
Other Benefits [Member] \| Hedge Funds [Member]
Actual return on plan assets:
Fair value of plan assets — end of year	11.5	24.6
Other Benefits [Member] \| Private Equity Funds [Member]
Actual return on plan assets:
Fair value of plan assets — end of year	6.2	6.0
Other Benefits [Member] \| Structured Credit [Member]
Actual return on plan assets:
Fair value of plan assets — end of year	6.1	13.5
Other Benefits [Member] \| Real Estate [Member]
Actual return on plan assets:
Fair value of plan assets — end of year	8.7	13.2
Significant Unobservable Inputs (Level 3) [Member] \| Other Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	57.3	57.8
Actual return on plan assets:
Relating to assets still held at the reporting date	2.8	7.5
Acquired through business combinations	0.1	48.0
Sales	(29.6)	(53.6)
Fair value of plan assets — end of year	32.5	57.3
Significant Unobservable Inputs (Level 3) [Member] \| Other Benefits [Member] \| Hedge Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	24.6	23.2
Actual return on plan assets:
Relating to assets still held at the reporting date	0.5	2.1
Acquired through business combinations	0	22.5
Sales	(14.2)	(22.5)
Fair value of plan assets — end of year	11.5	24.6
Significant Unobservable Inputs (Level 3) [Member] \| Other Benefits [Member] \| Private Equity Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	6.0	6.2
Actual return on plan assets:
Relating to assets still held at the reporting date	1.0	0.2
Acquired through business combinations	0.1	0.3
Sales	(1.3)	(1.1)
Fair value of plan assets — end of year	6.2	6.0
Significant Unobservable Inputs (Level 3) [Member] \| Other Benefits [Member] \| Structured Credit [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	13.5	12.5
Actual return on plan assets:
Relating to assets still held at the reporting date	0.4	2.4
Acquired through business combinations	0	11.0
Sales	(8.2)	(11.0)
Fair value of plan assets — end of year	6.1	13.5
Significant Unobservable Inputs (Level 3) [Member] \| Other Benefits [Member] \| Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets — beginning of year	13.2	15.9
Actual return on plan assets:
Relating to assets still held at the reporting date	0.9	2.8
Acquired through business combinations	0	14.2
Sales	(5.9)	(19.0)
Fair value of plan assets — end of year	$ 8.7	$ 13.2