Pension and Other Postretirement Employee Benefits (OPEB) Plans - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) corporate_bond	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Market-related value of assets held in trust, realized and unrealized gains or losess, included in preceding period, related to vesting percentage	25.00%
Fair value of assets	$ 14	$ 28
Assumed discount rate, number of corporate bonds used to derive yield curve | corporate_bond	490
Maximum amount employee may contribute if earnings are less that IRS threshold	75.00%
Percent of employees pay eligible for contribution to plan, minimum	1.00%
Percent of employees pay eligible for contribution to plan, maximum	20.00%
Percent of employees pay eligible to be matched by employer	6.00%
Employer contributions to the thrift plan	$ 46	33	$ 33
Pension costs
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	285	285	320
Employer contributions	19	0	0
Expected future employer contributions to retirement plan	25
Pension costs | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at net asset value	285	285
Pension costs | Cash commingled trusts | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at net asset value	6	4
OPEB costs
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	10	12	29
Employer contributions	8	9	$ 9
Expected future employer contributions to retirement plan	8
OPEB costs | Cash commingled trusts | Fair Value, Recurring
Defined Benefit Plan Disclosure [Line Items]
Total assets measured at net asset value	7	9
OPEB costs | Municipal Bond and Cash Equivalent Mutual Fund | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 3	$ 3
Qualified Plan
Defined Benefit Plan Disclosure [Line Items]
Percent of employees contribution matched by employer	100.00%
Traditional Retirement Plan Formula of Retirement Plan
Defined Benefit Plan Disclosure [Line Items]
Percent of employees contribution matched by employer	75.00%