Trust Investments (Narrative) (Detail) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) Facility	Dec. 31, 2021 USD ($)
Schedule of Trust Investments [Line Items]
Number of Nuclear Facilities | Facility	5
Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Trust Investments [Line Items]
NDT Fund Foreign Currency	$ 2	$ 2
Debt Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Trust Investments [Line Items]
After tax amount of net unrealized gains recognized in AOCI	(40)
Debt Securities [Member] | Rabbi Trust [Member]
Schedule of Trust Investments [Line Items]
After tax amount of net unrealized gains recognized in AOCI	(10)
Equity Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Trust Investments [Line Items]
Unrealized Gains (Losses) on Equity Securities still held	(47)
Equity Securities [Member] | Rabbi Trust [Member]
Schedule of Trust Investments [Line Items]
Unrealized Gains (Losses) on Equity Securities still held	$ (1)