Summary of Significant Accounting Policies (Narrative) (Detail) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2022 USD ($) MW	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Significant Accounting Policies
Public utilities, allowance for funds used during construction, rate			2.70%	2.60%	2.60%
Utilities operating expense, maintenance and operations			$ 460	$ 417	$ 357
Turbine maintenance expense			20	20	19
Amount accrued annually for nuclear fuel outages				17
Nuclear refueling outage cost			1	24	23
Amount accrued annually for tree trimming and vegetation management	$ 28
Amount accrued for tree trimming and vegetation management				9
Tree trimming and vegetation management cost			33	9
Decommissioning liability, noncurrent			788
Payments to acquire investments to be held in decommissioning trust fund			3
Unbilled revenues			188	139
Unrecognized tax benefits			68	62	138	$ 132
Interest expense			2	21	7
Penalty expenses				7	4
Income taxes related to affiliated payable			47
Income taxes related to affiliated receivable				24
Margin liabilities with cash collateral			0	0
Margin assets with cash collateral			1	$ 11
Option to extend, existence, operating lease				true
Maximum [Member]
Significant Accounting Policies
Interest income			$ 1	$ 1	$ 1
Lease renewal term			70 years
Original term of leases			1 year
Minimum [Member]
Significant Accounting Policies
Lease renewal term			1 year
Accounts Receivable [Member] | Credit Concentration Risk [Member] | Residential Commercial And Industrial Customers [Member]
Significant Accounting Policies
Concentration risk percentage			4.00%
Turbine [Member]
Significant Accounting Policies
Utilities operating expense, maintenance and operations	$ 25	$ 18
Genco [Member]
Significant Accounting Policies
Power Generation Capacity Megawatts | MW			605