Employee Benefit Plans (AOCI and Regulatory Assets and Liabilities that have Not been Recognized as Components of Periodic Benefit (Credit) Cost) (Parenthetical) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	$ 2,200	$ 3,211
Amount included in AOCI		1,700	1,900
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Total	[1]	(369)	(112)
Amount included in AOCI		$ (155)	$ (40)

[1] As of December 31, 2021, of the $2.2 billion and $(369) million related to pension benefits and other postretirement benefits, $1.7 billion and $(155) million, respectively, are included in AOCI, with the remainder included in regulatory assets and liabilities. As of December 31, 2020,