Annual report pursuant to Section 13 and 15(d)

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

v3.19.3.a.u2
PENSION AND OTHER POSTRETIREMENT BENEFITS - VEBA (Effect of Fair Value Measurements Using Significant Unobservable Inputs (Level 3) on Changes in Other Benefit Plan Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Other Postretirement Benefits Plan [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year $ 240.2 $ 262.5
Actual return on plan assets:    
Fair value of plan assets — end of year 259.7 240.2
Other Postretirement Benefits Plan [Member] | Hedge Funds [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 11.4  
Actual return on plan assets:    
Fair value of plan assets — end of year 12.4 11.4
Other Postretirement Benefits Plan [Member] | Private Equity Funds [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 3.0  
Actual return on plan assets:    
Fair value of plan assets — end of year 1.7 3.0
Other Postretirement Benefits Plan [Member] | Structured Credit [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 8.5  
Actual return on plan assets:    
Fair value of plan assets — end of year 5.5 8.5
Other Postretirement Benefits Plan [Member] | Real Estate [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 13.1  
Actual return on plan assets:    
Fair value of plan assets — end of year 14.0 13.1
Significant Unobservable Inputs (Level 3) [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 229.1 215.6
Actual return on plan assets:    
Relating to assets still held at the reporting date (1.3) 12.5
Relating to assets sold during the period 30.6 4.0
Purchases 16.5 5.2
Sales (59.9) (8.2)
Fair value of plan assets — end of year 212.4 229.1
Significant Unobservable Inputs (Level 3) [Member] | Hedge Funds [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 37.2 37.4
Actual return on plan assets:    
Relating to assets still held at the reporting date 3.4 (0.2)
Relating to assets sold during the period 0.0 0.0
Purchases 0.0 0.0
Sales 0.0 0.0
Fair value of plan assets — end of year 40.2 37.2
Significant Unobservable Inputs (Level 3) [Member] | Private Equity Funds [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 42.6 39.8
Actual return on plan assets:    
Relating to assets still held at the reporting date (1.0) 1.4
Relating to assets sold during the period 1.2 4.0
Purchases 16.5 5.2
Sales (9.3) (7.8)
Fair value of plan assets — end of year 49.5 42.6
Significant Unobservable Inputs (Level 3) [Member] | Real Estate [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 70.5 65.5
Actual return on plan assets:    
Relating to assets still held at the reporting date (4.2) 5.4
Relating to assets sold during the period 28.6 0.0
Purchases 0.0 0.0
Sales (23.8) (0.4)
Fair value of plan assets — end of year 70.4 70.5
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits Plan [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 36.0 35.2
Actual return on plan assets:    
Relating to assets still held at the reporting date 1.4 1.6
Relating to assets sold during the period 0.1 0.3
Purchases 0.0 0.0
Sales (3.9) (1.1)
Fair value of plan assets — end of year 33.6 36.0
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits Plan [Member] | Hedge Funds [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 11.4 11.4
Actual return on plan assets:    
Relating to assets still held at the reporting date 1.0 0.0
Relating to assets sold during the period 0.0 0.0
Purchases 0.0 0.0
Sales 0.0 0.0
Fair value of plan assets — end of year 12.4 11.4
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits Plan [Member] | Private Equity Funds [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 3.0 3.9
Actual return on plan assets:    
Relating to assets still held at the reporting date (0.6) (0.1)
Relating to assets sold during the period 0.0 0.3
Purchases 0.0 0.0
Sales (0.7) (1.1)
Fair value of plan assets — end of year 1.7 3.0
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits Plan [Member] | Structured Credit [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 8.5 7.9
Actual return on plan assets:    
Relating to assets still held at the reporting date 0.1 0.6
Relating to assets sold during the period 0.1 0.0
Purchases 0.0 0.0
Sales (3.2) 0.0
Fair value of plan assets — end of year 5.5 8.5
Significant Unobservable Inputs (Level 3) [Member] | Other Postretirement Benefits Plan [Member] | Real Estate [Member]    
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]    
Fair value of plan assets — beginning of year 13.1 12.0
Actual return on plan assets:    
Relating to assets still held at the reporting date 0.9 1.1
Relating to assets sold during the period 0.0 0.0
Purchases 0.0 0.0
Sales 0.0 0.0
Fair value of plan assets — end of year $ 14.0 $ 13.1