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, 2023 USD ($) MW	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Significant Accounting Policies
Public utilities, allowance for funds used during construction, rate			5.30%	2.70%	2.60%
Utilities operating expense, maintenance and operations			$ 436	$ 460	$ 417
Turbine maintenance expense			20	20	20
Amount accrued annually for nuclear fuel outages					17
Nuclear refueling outage cost			26	1	24
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			31	33	9
Decommissioning liability, noncurrent			808
Payments to acquire investments to be held in decommissioning trust fund			3
Unbilled revenues			176	188
Unrecognized tax benefits			62	68	62	$ 138
Interest expense			2	2	21
Penalty expenses					7
Income taxes related to affiliated payable			15	47
Margin liabilities with cash collateral			0	0
Margin assets with cash collateral			$ 0	1
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			10.00%
Turbine [Member]
Significant Accounting Policies
Utilities operating expense, maintenance and operations	$ 25	$ 18
GENCO [Member]
Significant Accounting Policies
Power Generation Capacity Megawatts | MW			605