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Pension and Other Postretirement Benefit Plans - Fair Values of Other Postretirement Benefit Plan Assets (Details) - Other Postretirement Benefits - USD ($) $ in Millions | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | $ 1,292 | $ 1,221 | $ 1,102
Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 39 | 59 |
Developed markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 402 | 374 |
Emerging markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 92 | 101 |
Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1 | 1 |
Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 8 |
Developed markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 290 | 258 |
Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 275 | 221 |
Corporate obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 191 | 196 |
Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 2 | 3 |
Level 1 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 326 | 325 |
Level 1 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 11 | 31 |
Level 1 | Developed markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 24 | 19 |
Level 1 | Emerging markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 16 |
Level 1 | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 1 | 1 |
Level 1 | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 1 | Developed markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 290 | 258 |
Level 1 | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 1 | Corporate obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 1 | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 2 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 468 | 428 |
Level 2 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 2 | Developed markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 2 | Emerging markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 2 | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 2 | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 8 |
Level 2 | Developed markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 2 | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 275 | 221 |
Level 2 | Corporate obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 191 | 196 |
Level 2 | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 2 | 3 |
Level 3 |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Developed markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Emerging markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Developed markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Corporate obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
Level 3 | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
NAV |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 498 | 468 |
NAV | Cash and cash equivalents |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 28 | 28 |
NAV | Developed markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 378 | 355 |
NAV | Emerging markets equities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 92 | 85 |
NAV | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value |  | 0 |
NAV | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
NAV | Developed markets |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
NAV | Government and agency obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
NAV | Corporate obligations |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | 0 | 0 |
NAV | Mortgage and asset-backed securities |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |
Plan assets at fair value | $ 0 | $ 0 |

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