Retirement Benefits - Components of Accumulated Other Comprehensive Income and Regulatory Assets (Liabilities) related to Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended	11 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Feb. 01, 2022
Defined Benefit Plan Disclosure [Line Items]
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax	$ 10					$ 1,994
Defined benefit plan, amounts recognized in regulatory assets, before tax	$ 18	$ 14
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial loss (gain)			$ 523	$ (226)	$ (700)
Amortization of actuarial (loss) gain			(166)	(295)	(598)
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		(2,631)	0	(2,631)	0
Current year prior service cost			4	0	0
Amortization of prior service (cost) credit			(2)	(2)	(3)
Settlements			(20)	0	(27)
Total recognized in AOCI and regulatory assets (liabilities)			339	(3,154)	(1,328)
Defined benefit plan, amounts recognized in OCI, before tax			99	(2,719)	(747)
Defined benefit plan, amounts recognized in regulatory assets, before tax			240	(435)	(581)
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Current year actuarial loss (gain)			30	(271)	(270)
Amortization of actuarial (loss) gain			2	(12)	(37)
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		$ (43)	0	(43)	0
Current year prior service cost			0	0	0
Amortization of prior service (cost) credit			10	19	34
Settlements			0	0	(1)
Total recognized in AOCI and regulatory assets (liabilities)			42	(307)	(274)
Defined benefit plan, amounts recognized in OCI, before tax			4	(74)	(130)
Defined benefit plan, amounts recognized in regulatory assets, before tax			$ 38	$ (233)	$ (144)