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Employee Benefit Plans - Defined Benefit Plan, Information about Plan Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Settlements $ 0 $ (6)    
Equity securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     40.00%  
Fixed income securities        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     60.00%  
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 (5)    
Foreign government | 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 (1)    
Pension Benefits        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 3,563      
Fair value of plan assets - end of year 3,345 3,563    
Plan assets at fair value 3,345 3,563 $ 3,345 $ 3,563
Excluded investment payables     1 1
Defined Benefit Plan, Fair Value of Plan Assets, Excluded Interest Receivables       30
Pension Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 973      
Fair value of plan assets - end of year 739 973    
Plan assets at fair value 739 973 739 973
Pension Benefits | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2,049      
Fair value of plan assets - end of year 1,997 2,049    
Plan assets at fair value 1,997 2,049 1,997 2,049
Pension Benefits | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 161 167    
Realized gains,net 0 2    
Changes in unrealized gains (losses), net (2) 6    
Purchases 6 36    
Sales (14) (35)    
Transfers into Level 3 0 2    
Transfers out of Level 3   (11)    
Fair value of plan assets - end of year 151 161    
Plan assets at fair value 151 161 151 161
Pension Benefits | Short-term Investments [Member]        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     110 189
Pension Benefits | Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     50 21
Pension Benefits | Short-term Investments [Member] | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     60 168
Pension Benefits | Short-term Investments [Member] | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Defined Benefit Plan, Equity Securities, Common Stock [Member]        
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 1 1    
Plan assets at fair value 1 1 $ 1 1
Pension Benefits | Equity securities | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     35.00%  
Pension Benefits | Equity securities | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     5.00%  
Pension Benefits | Fixed income securities | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     70.00%  
Pension Benefits | Fixed income securities | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     50.00%  
Pension Benefits | Alternative assets | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     45.00%  
Pension Benefits | Alternative assets | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     0.00%  
Pension Benefits | Corporate        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     $ 1,677 1,563
Pension Benefits | Corporate | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Corporate | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     1,663 1,549
Pension Benefits | Corporate | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 14 13    
Realized gains,net 0 0    
Changes in unrealized gains (losses), net (1) 2    
Purchases 5 11    
Sales (4) (12)    
Transfers into Level 3 0 0    
Fair value of plan assets - end of year 14 14    
Plan assets at fair value in the fair value hierarchy     14 14
Plan assets at fair value 14 14 14 14
Pension Benefits | Residential mortgage-backed securities (RMBS)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     63 30
Pension Benefits | Residential mortgage-backed securities (RMBS) | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Residential mortgage-backed securities (RMBS) | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     62 28
Pension Benefits | Residential mortgage-backed securities (RMBS) | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 2 10    
Realized gains,net 0 0    
Changes in unrealized gains (losses), net 0 0    
Purchases 0 1    
Sales (1) (4)    
Transfers into Level 3 0 0    
Transfers out of Level 3 0      
Fair value of plan assets - end of year 1 2    
Plan assets at fair value in the fair value hierarchy     1 2
Plan assets at fair value 2 2 1 2
Pension Benefits | U.S. Treasuries        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     130 77
Pension Benefits | U.S. Treasuries | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     10 3
Pension Benefits | U.S. Treasuries | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     120 74
Pension Benefits | U.S. Treasuries | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Foreign government        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     17 17
Pension Benefits | Foreign government | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Foreign government | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     15 16
Pension Benefits | Foreign government | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1 1    
Realized gains,net 0 0    
Changes in unrealized gains (losses), net 0 0    
Purchases 1 0    
Sales 0 0    
Transfers into Level 3 0 0    
Transfers out of Level 3 0      
Fair value of plan assets - end of year 2 1    
Plan assets at fair value in the fair value hierarchy     2 1
Plan assets at fair value 2 1 2 1
Pension Benefits | CMBS        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     22 30
Pension Benefits | CMBS | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | CMBS | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     22 28
Pension Benefits | CMBS | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 2
Pension Benefits | Other Fixed Income [Member]        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     53 99
Pension Benefits | Other Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Other Fixed Income [Member] | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     52 97
Pension Benefits | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     1 2
Pension Benefits | Mortgage loans        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     133 140
Pension Benefits | Mortgage loans | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Mortgage loans | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Mortgage loans | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 140 121    
Realized gains,net 0 0    
Changes in unrealized gains (losses), net (1) 2    
Purchases 0 17    
Sales (6) 0    
Transfers into Level 3 0 0    
Transfers out of Level 3 0      
Fair value of plan assets - end of year 133 140    
Plan assets at fair value in the fair value hierarchy     133 140
Plan assets at fair value 140 140 133 140
Pension Benefits | Other investments | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 4 22    
Realized gains,net 0 2    
Changes in unrealized gains (losses), net 0 2    
Purchases 0 7    
Sales (3) (19)    
Transfers into Level 3 0 2    
Transfers out of Level 3   (11)    
Fair value of plan assets - end of year 1 4    
Plan assets at fair value 4 4 1 4
Pension Benefits | Large-cap domestic        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     379 684
Pension Benefits | Large-cap domestic | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     376 595
Pension Benefits | Large-cap domestic | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     3 89
Pension Benefits | Large-cap domestic | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | Mid-cap domestic        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy       11
Pension Benefits | Mid-cap domestic | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy       11
Pension Benefits | Mid-cap domestic | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy       0
Pension Benefits | Mid-cap domestic | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy       0
Pension Benefits | International        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     303 343
Pension Benefits | International | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     303 343
Pension Benefits | International | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     0 0
Pension Benefits | International | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
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        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     2,887 3,183
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     739 973
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     1,997 2,049
Pension Benefits | Total pension plan assets at fair value, in the fair value hierarchy | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at fair value in the fair value hierarchy     151 161
Pension Benefits | Private Market Alternatives        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value     272 168
Pension Benefits | Private Market Alternatives | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value    
Pension Benefits | Private Market Alternatives | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value    
Pension Benefits | Private Market Alternatives | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value    
Pension Benefits | Hedge funds        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value     186 212
Pension Benefits | Hedge funds | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value    
Pension Benefits | Hedge funds | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value    
Pension Benefits | Hedge funds | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Plan assets at net asset value    
Other Postretirement Benefits        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 113      
Fair value of plan assets - end of year 85 113    
Plan assets at fair value 85 113 85 113
Excluded investment payables     1 0
Defined Benefit Plan, Fair Value of Plan Assets, Excluded Interest Receivables       1
Other Postretirement Benefits | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 35      
Fair value of plan assets - end of year 33 35    
Plan assets at fair value 33 35 33 35
Other Postretirement Benefits | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 77      
Fair value of plan assets - end of year 52 77    
Plan assets at fair value 52 77 52 77
Other Postretirement Benefits | Significant Unobservable Inputs (Level 3)        
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   1    
Plan assets at fair value 1 1   1
Other Postretirement Benefits | Short-term Investments [Member]        
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 4 4    
Plan assets at fair value 4 4 4 4
Other Postretirement Benefits | Short-term Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1)        
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 4 4    
Plan assets at fair value 4 4 4 4
Other Postretirement Benefits | Short-term Investments [Member] | Significant Observable Inputs (Level 2)        
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    
Plan assets at fair value 0 0 0 0
Other Postretirement Benefits | Defined Benefit Plan, Equity Securities, Common Stock [Member]        
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    
Plan assets at fair value 0 0 $ 0 0
Other Postretirement Benefits | Equity securities | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     45.00%  
Other Postretirement Benefits | Equity securities | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     15.00%  
Other Postretirement Benefits | Fixed income securities | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     85.00%  
Other Postretirement Benefits | Fixed income securities | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     55.00%  
Other Postretirement Benefits | Alternative assets | Maximum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     0.00%  
Other Postretirement Benefits | Alternative assets | Minimum        
Defined Benefit Plan Disclosure [Line Items]        
Target asset allocation     0.00%  
Other Postretirement Benefits | Corporate        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 25      
Fair value of plan assets - end of year 19 25    
Plan assets at fair value 19 25 $ 19 25
Other Postretirement Benefits | Corporate | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 25      
Fair value of plan assets - end of year 19 25    
Plan assets at fair value 19 25 19 25
Other Postretirement Benefits | Corporate | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 0 1    
Purchases   1    
Sales   2    
Fair value of plan assets - end of year   0    
Plan assets at fair value 0 1   0
Other Postretirement Benefits | Residential mortgage-backed securities (RMBS)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 17      
Fair value of plan assets - end of year 15 17    
Plan assets at fair value 15 17 15 17
Other Postretirement Benefits | Residential mortgage-backed securities (RMBS) | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 17      
Fair value of plan assets - end of year 15 17    
Plan assets at fair value 15 17 15 17
Other Postretirement Benefits | Residential mortgage-backed securities (RMBS) | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 0 1    
Settlements   1    
Fair value of plan assets - end of year   0    
Plan assets at fair value 0 1   0
Other Postretirement Benefits | U.S. Treasuries        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 26      
Fair value of plan assets - end of year 19 26    
Plan assets at fair value 19 26 19 26
Other Postretirement Benefits | U.S. Treasuries | Quoted Prices in Active Markets for Identical Assets (Level 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 6 1    
Plan assets at fair value 6 1 6 1
Other Postretirement Benefits | U.S. Treasuries | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 25      
Fair value of plan assets - end of year 13 25    
Plan assets at fair value 13 25 13 25
Other Postretirement Benefits | Foreign government        
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 1 1    
Plan assets at fair value 1 1 1 1
Other Postretirement Benefits | Foreign government | Significant Observable Inputs (Level 2)        
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 1 1    
Plan assets at fair value 1 1 1 1
Other Postretirement Benefits | CMBS        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 5      
Fair value of plan assets - end of year 2 5    
Plan assets at fair value 2 5 2 5
Other Postretirement Benefits | CMBS | Significant Observable Inputs (Level 2)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 5      
Fair value of plan assets - end of year 2 5    
Plan assets at fair value 2 5 2 5
Other Postretirement Benefits | Other Fixed Income [Member]        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 5      
Fair value of plan assets - end of year 2 5    
Plan assets at fair value 2 5 2 5
Other Postretirement Benefits | Other Fixed Income [Member] | Significant Observable Inputs (Level 2)        
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 2 4    
Plan assets at fair value 2 4 2 4
Other Postretirement Benefits | Other Fixed Income [Member] | Significant Unobservable Inputs (Level 3)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 1      
Purchases   1    
Sales 1      
Transfers out of Level 3   1    
Fair value of plan assets - end of year 0 1    
Plan assets at fair value 1 1 0 1
Other Postretirement Benefits | Large-cap        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 30      
Fair value of plan assets - end of year 23 30    
Plan assets at fair value 23 30 23 30
Other Postretirement Benefits | Large-cap | Quoted Prices in Active Markets for Identical Assets (Level 1)        
Pension Plan Asset Fair Value Measurements Using Significant Unobservable Inputs (Level 3)        
Fair value of plan assets - beginning of year 30      
Fair value of plan assets - end of year 23 30    
Plan assets at fair value 23 30 23 30
Other Postretirement Benefits | Large-cap | Significant Observable Inputs (Level 2)        
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    
Plan assets at fair value $ 0 $ 0 $ 0 $ 0