Other Postretirement Benefits - Schedule of Fair Values of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	$ 525	$ 465
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	1,150	1,115	$ 1,026	$ 885
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Total investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	875	842
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Equity
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	474	448
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Other Fixed Income Debt
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	379	367
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	22	27
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Funds For Retiree Health Benefits
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	210	213
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Investments, Including Funds For Retiree Health Benefit
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	1,085	1,055
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Funds For Retiree Health Benefits Measured At Net Asset Value
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	48	41
Other Postretirement Benefits | Fair Value, Inputs, Level 1 and 2 | Pending Activities
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	17	19
Other Postretirement Benefits | Level 1 | Total investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	0	0
Other Postretirement Benefits | Level 1 | Equity
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	0	0
Other Postretirement Benefits | Level 1 | Other Fixed Income Debt
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	0	0
Other Postretirement Benefits | Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	0	0
Other Postretirement Benefits | Level 1 | Funds For Retiree Health Benefits
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	110	116
Other Postretirement Benefits | Level 1 | Investments, Including Funds For Retiree Health Benefit
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	110	116
Other Postretirement Benefits | Level 2 | Total investments
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	875	842
Other Postretirement Benefits | Level 2 | Equity
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	474	448
Other Postretirement Benefits | Level 2 | Other Fixed Income Debt
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	379	367
Other Postretirement Benefits | Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	22	27
Other Postretirement Benefits | Level 2 | Funds For Retiree Health Benefits
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	100	97
Other Postretirement Benefits | Level 2 | Investments, Including Funds For Retiree Health Benefit
Defined Benefit Plan Disclosure [Line Items]
Total fair value of plan net assets	$ 975	$ 939