Fair Value Measurements - Postretirement Health Care Plan (Details) - Postretirement Health Care Benefits Plan - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	$ 134	$ 134	$ 186
Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	134	134
Recurring | Total investment securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	133	132
Recurring | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	1	2
Recurring | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	69	71
Recurring | Government fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	8	7
Recurring | Corporate fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	38	39
Recurring | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	10	8
Recurring | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	7	5
Recurring | Accrued income receivable
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	1	2
Level 1 | Recurring | Total investment securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	60	59
Level 1 | Recurring | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	1	2
Level 1 | Recurring | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	49	49
Level 1 | Recurring | Government fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 1 | Recurring | Corporate fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 1 | Recurring | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	10	8
Level 1 | Recurring | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 2 | Recurring | Total investment securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	66	68
Level 2 | Recurring | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 2 | Recurring | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	20	22
Level 2 | Recurring | Government fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	8	7
Level 2 | Recurring | Corporate fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	38	39
Level 2 | Recurring | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 2 | Recurring | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 3 | Recurring | Total investment securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	7	5
Level 3 | Recurring | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 3 | Recurring | Commingled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 3 | Recurring | Government fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 3 | Recurring | Corporate fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 3 | Recurring | Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	0	0
Level 3 | Recurring | Private assets
Defined Benefit Plan Disclosure [Line Items]
Fair value plan assets	$ 7	$ 5