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Employee Benefit Plans - Defined Benefit Plan, Information about Plan Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements $ 0 $ 0    
Corporate | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements 0 0    
Residential mortgage-backed securities (RMBS) | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements 0 0    
Foreign government/government agencies | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements 0 0    
Mortgage loans | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements 0 0    
Other investments | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements 0 0    
Pension Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 3,345 3,345 $ 3,874 $ 3,345
Defined Benefit Plan, Fair Value of Plan Assets, Excluded Investment Payables     40 1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 3,345      
Fair value of plan assets - end of year 3,874 3,345    
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 739 739 724 739
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 739      
Fair value of plan assets - end of year 724 739    
Pension Benefits | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 1,997 1,997 2,420 1,997
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1,997      
Fair value of plan assets - end of year 2,420 1,997    
Pension Benefits | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 151 151 $ 160 151
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 151 161    
Realized gains,net 3 0    
Changes in unrealized gains, net 6 (2)    
Purchases 7 6    
Sales (11) (14)    
Transfers into Level 3 4 0    
Transfers out of Level 3   0    
Fair value of plan assets - end of year 160 151    
Pension Benefits | Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     40.00%  
Pension Benefits | Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     60.00%  
Pension Benefits | Short-term Investments [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     $ 88 110
Pension Benefits | Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     34 50
Pension Benefits | Short-term Investments [Member] | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     54 60
Pension Benefits | Short-term Investments [Member] | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Corporate        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     2,085 1,677
Pension Benefits | Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Corporate | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     2,058 1,663
Pension Benefits | Corporate | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     27 14
Plan assets at fair value 14 14 27 14
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 14 14    
Realized gains,net 3 0    
Changes in unrealized gains, net 2 (1)    
Purchases 7 5    
Sales (3) 4    
Transfers into Level 3 4 0    
Fair value of plan assets - end of year 27 14    
Pension Benefits | Residential mortgage-backed securities (RMBS)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     61 63
Pension Benefits | Residential mortgage-backed securities (RMBS) | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Residential mortgage-backed securities (RMBS) | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     61 62
Pension Benefits | Residential mortgage-backed securities (RMBS) | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 1
Plan assets at fair value 0 2 0 1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1 2    
Realized gains,net 0 0    
Changes in unrealized gains, net 0 0    
Purchases 0 0    
Sales (1) (1)    
Transfers into Level 3 0 0    
Transfers out of Level 3 0 0    
Fair value of plan assets - end of year 0 1    
Pension Benefits | U.S. Treasuries        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     101 130
Pension Benefits | U.S. Treasuries | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 10
Pension Benefits | U.S. Treasuries | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     101 120
Pension Benefits | U.S. Treasuries | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Foreign government/government agencies        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     18 17
Pension Benefits | Foreign government/government agencies | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Foreign government/government agencies | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     17 15
Pension Benefits | Foreign government/government agencies | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     1 2
Plan assets at fair value 2 2 1 2
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2 1    
Realized gains,net 0 0    
Changes in unrealized gains, net 0 0    
Purchases 0 1    
Sales (1) 0    
Transfers into Level 3 0 0    
Transfers out of Level 3 0 0    
Fair value of plan assets - end of year 1 2    
Pension Benefits | CMBS        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     32 22
Pension Benefits | CMBS | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | CMBS | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     32 22
Pension Benefits | CMBS | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Other Fixed Income [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     97 53
Pension Benefits | Other Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Other Fixed Income [Member] | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     96 52
Pension Benefits | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     1 1
Pension Benefits | Mortgage loans        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     131 133
Pension Benefits | Mortgage loans | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Mortgage loans | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Mortgage loans | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     131 133
Plan assets at fair value 131 140 131 133
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 133 140    
Realized gains,net 0 0    
Changes in unrealized gains, net 4 (1)    
Purchases 0 0    
Sales (6) 6    
Transfers into Level 3 0 0    
Transfers out of Level 3 0      
Fair value of plan assets - end of year 131 133    
Pension Benefits | Domestic        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     430 379
Pension Benefits | Domestic | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     429 376
Pension Benefits | Domestic | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     1 3
Pension Benefits | Domestic | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | International        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     261 303
Pension Benefits | International | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     261 303
Pension Benefits | International | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | International | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     3,304 2,887
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     724 739
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     2,420 1,997
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value in the fair value hierarchy     160 151
Pension Benefits | Private Market Alternatives        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value     358 272
Pension Benefits | Private Market Alternatives | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value      
Pension Benefits | Private Market Alternatives | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value      
Pension Benefits | Private Market Alternatives | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value      
Pension Benefits | Hedge funds        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value     212 186
Pension Benefits | Hedge funds | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value      
Pension Benefits | Hedge funds | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value      
Pension Benefits | Hedge funds | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at net asset value      
Pension Benefits | Other investments | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 1 4 1 1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1 4    
Realized gains,net 0 0    
Changes in unrealized gains, net 0 0    
Purchases 0 0    
Sales 0 3    
Transfers into Level 3 0 0    
Transfers out of Level 3   0    
Fair value of plan assets - end of year 1 1    
Pension Benefits | Defined Benefit Plan, Equity Securities, Common Stock [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 1   1  
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - end of year 1      
Other Postretirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 85 85 75 85
Defined Benefit Plan, Fair Value of Plan Assets, Excluded Investment Payables       1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 85      
Fair value of plan assets - end of year 75 85    
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 33 33 22 33
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 33      
Fair value of plan assets - end of year 22 33    
Other Postretirement Benefits | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 52 52 $ 53 52
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 52      
Fair value of plan assets - end of year 53 52    
Other Postretirement Benefits | Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     30.00%  
Other Postretirement Benefits | Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     70.00%  
Other Postretirement Benefits | Short-term Investments [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 4 4 $ 3 4
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 4      
Fair value of plan assets - end of year 3 4    
Other Postretirement Benefits | Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 4 4 3 4
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 4      
Fair value of plan assets - end of year 3 4    
Other Postretirement Benefits | Short-term Investments [Member] | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 0 0 0 0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 0      
Fair value of plan assets - end of year 0 0    
Other Postretirement Benefits | Corporate        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 19 19 18 19
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 19      
Fair value of plan assets - end of year 18 19    
Other Postretirement Benefits | Corporate | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 19 19 18 19
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 19      
Fair value of plan assets - end of year 18 19    
Other Postretirement Benefits | Corporate | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 0 1   0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 0 1    
Fair value of plan assets - end of year   0    
Other Postretirement Benefits | Residential mortgage-backed securities (RMBS)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 15 15 12 15
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 15      
Fair value of plan assets - end of year 12 15    
Other Postretirement Benefits | Residential mortgage-backed securities (RMBS) | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 15 15 12 15
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 15      
Fair value of plan assets - end of year 12 15    
Other Postretirement Benefits | U.S. Treasuries        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 19 19 20 19
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 19      
Fair value of plan assets - end of year 20 19    
Other Postretirement Benefits | U.S. Treasuries | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 6 6   6
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 6      
Fair value of plan assets - end of year   6    
Other Postretirement Benefits | U.S. Treasuries | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 13 13 20 13
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 13      
Fair value of plan assets - end of year 20 13    
Other Postretirement Benefits | Foreign government/government agencies        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 1 1 0 1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1      
Fair value of plan assets - end of year 0 1    
Other Postretirement Benefits | Foreign government/government agencies | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 1 1 0 1
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1      
Fair value of plan assets - end of year 0 1    
Other Postretirement Benefits | CMBS        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 2 2 1 2
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2      
Fair value of plan assets - end of year 1 2    
Other Postretirement Benefits | CMBS | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 2 2 1 2
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2      
Fair value of plan assets - end of year 1 2    
Other Postretirement Benefits | Other Fixed Income [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 2 2 2 2
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2      
Fair value of plan assets - end of year 2 2    
Other Postretirement Benefits | Other Fixed Income [Member] | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 2 2 2 2
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2      
Fair value of plan assets - end of year 2 2    
Other Postretirement Benefits | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3)        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Plan Assets Level 3 Reconciliation, Decrease for Sale   1    
Other Postretirement Benefits | Large-cap        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 23 23 19 23
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 23      
Fair value of plan assets - end of year 19 23    
Other Postretirement Benefits | Large-cap | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 23 23 19 23
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 23      
Fair value of plan assets - end of year 19 23    
Other Postretirement Benefits | Large-cap | Significant Observable Inputs (Level 2)        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 0 0 0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 0      
Fair value of plan assets - end of year 0    
Other Postretirement Benefits | Defined Benefit Plan, Equity Securities, Common Stock [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Plan assets at fair value 0 0 $ 0 $ 0
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 0      
Fair value of plan assets - end of year $ 0 $ 0    
Minimum | Pension Benefits | Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     5.00%  
Minimum | Pension Benefits | Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     50.00%  
Minimum | Pension Benefits | Alternative assets        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     0.00%  
Minimum | Other Postretirement Benefits | Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     15.00%  
Minimum | Other Postretirement Benefits | Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     55.00%  
Minimum | Other Postretirement Benefits | Alternative assets        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     0.00%  
Maximum | Pension Benefits | Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     35.00%  
Maximum | Pension Benefits | Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     70.00%  
Maximum | Pension Benefits | Alternative assets        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     45.00%  
Maximum | Other Postretirement Benefits | Equity Securities [Member]        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     45.00%  
Maximum | Other Postretirement Benefits | Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     85.00%  
Maximum | Other Postretirement Benefits | Alternative assets        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     0.00%