Employee Benefits - Fair Value of Plan Assets and Liabilities (Details) - Combined Pension Plan - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	$ 8,531	$ 10,546	$ 10,493	$ 10,033
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	11	8	22
NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	2,690	3,368
Investment Grade Bonds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	127	352
High Yield Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	6	6	5
High Yield Bonds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	70	25
U.S. Stocks | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	5	2	1
U.S. Stocks | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	71	192
Non-U.S. Stocks | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	398	308
Emerging Market Stocks | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	11	81
Private Equity | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	348	283
Private Debt | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0	$ 16
Private Debt | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	495	505
Market Neutral Hedge Funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	141	222
Directional Hedge Funds | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	241	254
Real Estate | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	420	543
Multi-Asset Strategies | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	38	375
Cash equivalents and short-term investments | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	330	228
Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	8,531	10,546
Fair Value, Measurements, Recurring | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	2,690	3,368
Fair Value, Measurements, Recurring | Total Excluding Investments Valued at NAV | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	6,034	7,179
Fair Value, Measurements, Recurring | Total Excluding Investments Valued at NAV | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	1,555	2,389
Fair Value, Measurements, Recurring | Total Excluding Investments Valued at NAV | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	4,468	4,782
Fair Value, Measurements, Recurring | Total Excluding Investments Valued at NAV | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	11	8
Fair Value, Measurements, Recurring | Investment Grade Bonds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	4,606	4,792
Fair Value, Measurements, Recurring | Investment Grade Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	862	726
Fair Value, Measurements, Recurring | Investment Grade Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	3,744	4,066
Fair Value, Measurements, Recurring | Investment Grade Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | High Yield Bonds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	178	268
Fair Value, Measurements, Recurring | High Yield Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | High Yield Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	172	262
Fair Value, Measurements, Recurring | High Yield Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	6	6
Fair Value, Measurements, Recurring | Emerging Market Bonds | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	233	390
Fair Value, Measurements, Recurring | Emerging Market Bonds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	64	218
Fair Value, Measurements, Recurring | Emerging Market Bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	169	172
Fair Value, Measurements, Recurring | Emerging Market Bonds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | U.S. Stocks | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	338	655
Fair Value, Measurements, Recurring | U.S. Stocks | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	330	653
Fair Value, Measurements, Recurring | U.S. Stocks | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	3	0
Fair Value, Measurements, Recurring | U.S. Stocks | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	5	2
Fair Value, Measurements, Recurring | Non-U.S. Stocks | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	256	594
Fair Value, Measurements, Recurring | Non-U.S. Stocks | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	256	593
Fair Value, Measurements, Recurring | Non-U.S. Stocks | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	1
Fair Value, Measurements, Recurring | Non-U.S. Stocks | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | Multi-Asset Strategies | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	41	199
Fair Value, Measurements, Recurring | Multi-Asset Strategies | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	41	199
Fair Value, Measurements, Recurring | Multi-Asset Strategies | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | Multi-Asset Strategies | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | Derivatives | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	1	(1)
Fair Value, Measurements, Recurring | Derivatives | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | Derivatives | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	1	(1)
Fair Value, Measurements, Recurring | Derivatives | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0	0
Fair Value, Measurements, Recurring | Repurchase Agreements | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	(193)
Fair Value, Measurements, Recurring | Repurchase Agreements | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0
Fair Value, Measurements, Recurring | Repurchase Agreements | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	(193)
Fair Value, Measurements, Recurring | Repurchase Agreements | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	0
Fair Value, Measurements, Recurring | Cash equivalents and short-term investments | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	381	281
Fair Value, Measurements, Recurring | Cash equivalents and short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	2	0
Fair Value, Measurements, Recurring | Cash equivalents and short-term investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	379	281
Fair Value, Measurements, Recurring | Cash equivalents and short-term investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets (liabilities)	$ 0	$ 0