Derivative Financial Instruments (Derivatives in Cash Flow Hedging Relationships) (Detail) - Cash Flow Hedging [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Derivative [Line Items]
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1]	$ 5	$ 7
Interest Rate Contract [Member]
Derivative [Line Items]
Increase (Decrease) in Derivatives Subject to Regulatory Treatment	[1]	$ 5	$ 7

[1] Represents net derivative activity deferred into and amortized out of regulatory assets/liabilities. Amounts deferred into regulatory assets/ liabilities have no associated effect in the Consolidated Statements of Comprehensive Income.