Pension and Other Postretirement Benefits - Fair Value Measurements (Details) - Pension Benefits - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	$ 3,191	$ 3,347	$ 3,176
Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	2,118	2,134
Fair Value, Recurring | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	88	8
Fair Value, Recurring | U.S. treasury securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	164	78
Fair Value, Recurring | Government-related securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	175	167
Fair Value, Recurring | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	1,448	1,634
Fair Value, Recurring | Mortgage-backed and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	76	56
Fair Value, Recurring | U.S. large capitalization
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	72	82
Fair Value, Recurring | U.S. small capitalization
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	81	79
Fair Value, Recurring | Other
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	14	30
Fair Value, Recurring | Level 1
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	400	247
Fair Value, Recurring | Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	83	8
Fair Value, Recurring | Level 1 | U.S. treasury securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	164	78
Fair Value, Recurring | Level 1 | Government-related securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 1 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 1 | Mortgage-backed and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 1 | U.S. large capitalization
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	72	82
Fair Value, Recurring | Level 1 | U.S. small capitalization
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	81	79
Fair Value, Recurring | Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 2
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	1,718	1,887
Fair Value, Recurring | Level 2 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	5	0
Fair Value, Recurring | Level 2 | U.S. treasury securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 2 | Government-related securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	175	167
Fair Value, Recurring | Level 2 | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	1,448	1,634
Fair Value, Recurring | Level 2 | Mortgage-backed and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	76	56
Fair Value, Recurring | Level 2 | U.S. large capitalization
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 2 | U.S. small capitalization
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	0	0
Fair Value, Recurring | Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	14	30
Fair Value, Recurring | Fair Value Measured at net asset value | Common collective funds
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	1,013	1,149
Fair Value, Recurring | Fair Value Measured at net asset value | Limited partnerships
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	18	18
Fair Value, Recurring | Fair Value Measured at net asset value | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Investments, at fair value	$ 42	$ 46