Summary of Significant Accounting Policies (Narrative) (Detail)	3 Months Ended	12 Months Ended			16 Months Ended	17 Months Ended
	Sep. 30, 2021 USD ($)	Dec. 31, 2025 USD ($) MW	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2025 USD ($) MW	Dec. 31, 2025 USD ($) MW	Dec. 31, 2022 USD ($)
Significant Accounting Policies
Public utilities, allowance for funds used during construction, rate		5.30%	5.30%	5.30%
Utilities operating expense, maintenance and operations		$ 507,000,000	$ 492,000,000	$ 436,000,000
Turbine maintenance expense		30,000,000	16,000,000	20,000,000
Amount accrued annually for nuclear fuel outages					$ 24,000,000	$ 17,000,000
Nuclear refueling outage cost		0	42,000,000	26,000,000
Amount accrued annually for tree trimming and vegetation management					34,000,000	28,000,000
Tree trimming and vegetation management cost		31,000,000	29,000,000	31,000,000
Decommissioning liability, noncurrent		911,000,000			911,000,000	911,000,000
Payments to acquire investments to be held in decommissioning trust fund		3,000,000
Unbilled revenues		191,000,000	176,000,000		191,000,000	191,000,000
Deferred tax asset,valuation allowance		2,000,000	0		2,000,000	2,000,000
Unrecognized tax benefits		0	38,000,000	$ 62,000,000	0	0	$ 68,000,000
Interest expense			12,000,000
Income taxes related to affiliated payable		4,000,000	12,000,000
Margin liabilities with cash collateral		0	0		0	0
Margin assets with cash collateral		$ 0	$ 0		$ 0	$ 0
Option to extend, existence, operating lease		true
Maximum [Member]
Significant Accounting Policies
Lease renewal term		70 years			70 years	70 years
Original term of leases		1 year			1 year	1 year
Minimum [Member]
Significant Accounting Policies
Lease renewal term		1 year			1 year	1 year
Accounts Receivable [Member] \| Credit Concentration Risk [Member] \| Residential Commercial And Industrial Customers [Member]
Significant Accounting Policies
Concentration risk percentage		5.00%
Turbine [Member]
Significant Accounting Policies
Utilities operating expense, maintenance and operations	$ 25,000,000
GENCO [Member]
Significant Accounting Policies
Power Generation Capacity Megawatts \| MW		605			605	605

DOMINION ENERGY SOUTH CAROLINA, INC. 10-K