Retirement Benefits - Gross Accumulated Other Comprehensive Loss and Regulatory Assets (Liabilities) not Recognized as Components of Periodic Benefit Cost (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Pension Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	$ 19	$ 32
Actuarial loss (gain)	3,611	6,752
Total	3,630	6,784
Benefits included in accumulated other comprehensive income	873	3,592
Benefits included in regulatory assets (liabilities)	2,757	3,192
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service cost (credit)	(55)	(111)
Actuarial loss (gain)	(133)	230
Total	(188)	119
Benefits included in accumulated other comprehensive income	(21)	53
Benefits included in regulatory assets (liabilities)	$ (167)	$ 66