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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% |

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