Benefit Plans - Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	$ 2,466	$ 1,865	$ 1,902
Significant Unobservable Inputs (Level 3) | Corporate bonds and other fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	2,387	1,791	1,836
Significant Unobservable Inputs (Level 3) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	74	70	62
Significant Unobservable Inputs (Level 3) | Private equity and other
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5	4	$ 4
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	12,724	12,802
Pension Plans | Total Fair Value
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	10,342	10,389
Pension Plans | Total Fair Value | Total equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	1,552	2,230
Pension Plans | Total Fair Value | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	4	4
Pension Plans | Total Fair Value | Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	3	1
Pension Plans | Total Fair Value | Pooled funds - equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	1,545	2,225
Pension Plans | Total Fair Value | Total fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	8,368	7,822
Pension Plans | Total Fair Value | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	3,777	4,340
Pension Plans | Total Fair Value | Pooled funds - fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	648	622
Pension Plans | Total Fair Value | Corporate bonds and other fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	3,943	2,860
Pension Plans | Total Fair Value | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	251	212
Pension Plans | Total Fair Value | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	4	3
Pension Plans | Total Fair Value | Other
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	162	5
Pension Plans | Total Fair Value | Cash
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5	117
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	2,075	2,014
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Total equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	1,091	1,004
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	4	4
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	3	1
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	1,084	999
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Total fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	644	757
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	56	60
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	449	439
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds and other fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	139	258
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	179	142
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	157	4
Pension Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	4	107
Pension Plans | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5,801	6,510
Pension Plans | Significant Other Observable Inputs (Level 2) | Total equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	461	1,226
Pension Plans | Significant Other Observable Inputs (Level 2) | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Other Observable Inputs (Level 2) | Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Other Observable Inputs (Level 2) | Pooled funds - equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	461	1,226
Pension Plans | Significant Other Observable Inputs (Level 2) | Total fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5,335	5,274
Pension Plans | Significant Other Observable Inputs (Level 2) | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	3,721	4,280
Pension Plans | Significant Other Observable Inputs (Level 2) | Pooled funds - fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	199	183
Pension Plans | Significant Other Observable Inputs (Level 2) | Corporate bonds and other fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	1,415	811
Pension Plans | Significant Other Observable Inputs (Level 2) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Other Observable Inputs (Level 2) | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Other Observable Inputs (Level 2) | Other
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	5	0
Pension Plans | Significant Other Observable Inputs (Level 2) | Cash
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	10
Pension Plans | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	2,466	1,865
Pension Plans | Significant Unobservable Inputs (Level 3) | Total equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Non-U.S. equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Pooled funds - equity securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Total fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	2,389	1,791
Pension Plans | Significant Unobservable Inputs (Level 3) | Government bonds
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Pooled funds - fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	0
Pension Plans | Significant Unobservable Inputs (Level 3) | Corporate bonds and other fixed-income securities
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	2,389	1,791
Pension Plans | Significant Unobservable Inputs (Level 3) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	72	70
Pension Plans | Significant Unobservable Inputs (Level 3) | Private equity
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	4	3
Pension Plans | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	0	1
Pension Plans | Significant Unobservable Inputs (Level 3) | Cash
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	1	0
Pension Plans | Investments measured at net asset value
Defined Benefit Plan Disclosure [Line Items]
Total investments at fair value	$ 2,382	$ 2,413