Retirement Benefits - Changes in Plan Assets Recognized in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Separation-related adjustment	$ 0	$ 2,664
Current year actuarial (gain) loss	509	11
Amortization of actuarial (loss) gain	(46)	(134)
Amortization of prior service (cost) credit	(1)	(1)
Settlements	0	(6)
Total recognized in AOCI	462	2,534
Prior service (credit) cost	9	10
Actuarial (gain) loss	2,985	2,524
Total	2,994	2,534
OPEB
Defined Benefit Plan Disclosure [Line Items]
Separation-related adjustment	0	22
Current year actuarial (gain) loss	94	(253)
Amortization of actuarial (loss) gain	14	1
Amortization of prior service (cost) credit	6	7
Settlements	0	0
Total recognized in AOCI	114	(223)
Prior service (credit) cost	(24)	(30)
Actuarial (gain) loss	(85)	(193)
Total	$ (109)	$ (223)

Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax, Current

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Other Comprehensive Income (Loss), Defined Benefit Plan, Transfer to Parent Company Due to Split

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- Definition

Amount, after tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount, after tax, of accumulated other comprehensive (income) loss for cost (credit) of benefit change attributable to participants' prior service from plan amendment or plan initiation of defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount, before tax, of increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan.

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Amount, before tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

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