Trust Investments (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Trust Investments [Line Items]
NDT Fund Foreign Currency	$ 2	$ 2
Decommissioning Liability, Noncurrent	1,200
Nuclear Decommissioning Trust (NDT) Fund [Member] | Minimum
Schedule of Trust Investments [Line Items]
Decommissioning Costs Including Contingencies	3,000
Nuclear Decommissioning Trust (NDT) Fund [Member] | Maximum [Member]
Schedule of Trust Investments [Line Items]
Decommissioning Costs Including Contingencies	3,400
Debt Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Trust Investments [Line Items]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent	8
Debt Securities [Member] | Rabbi Trust [Member]
Schedule of Trust Investments [Line Items]
Other Comprehensive Income (Loss), Available-for-sale Securities Adjustment, Net of Tax, Portion Attributable to Parent	3
Equity Securities [Member] | Nuclear Decommissioning Trust (NDT) Fund [Member]
Schedule of Trust Investments [Line Items]
Unrealized Gains (Losses) on Equity Securities still held	130
Equity Securities [Member] | Rabbi Trust [Member]
Schedule of Trust Investments [Line Items]
Unrealized Gains (Losses) on Equity Securities still held	$ 1