Debt instrument maturity year.

No definition available.

Name:	ck91882_DebtInstrumentMaturityYear
Namespace Prefix:	ck91882_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585

+ Details

Name:	us-gaap_RepaymentsOfLongTermDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_LetterOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ck91882_FirstMortgageBondsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ck91882_DESCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ck91882_TaxExemptFinancingsVariableRateDueTwoThousandAndThirtyEightMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=ck91882_GencoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ck91882_TaxExemptFinancingsThreePointSixTwoFiveAndFourDueTwoThousandAndTwentyEightAndTwoThousandThirtyThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=ck91882_ThreePointZeroFivePercentAffiliatedNoteMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-Term and Short-Term Debt (Schedule of Debt) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Redemption of remaining principal outstanding plus accrued interest	$ 0	$ 1,890	$ 825
Letter of Credit
Debt Instrument [Line Items]
Debt instrument, face amount	$ 68
First Mortgage Bonds \| Minimum [Member] \| DESC
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2021
Debt instrument, interest rate	3.22%
First Mortgage Bonds \| Maximum [Member] \| DESC
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2065
Debt instrument, interest rate	6.625%
Tax Exempt Financings Variable Rate Due 2038 \| DESC
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2038
Tax Exempt Financings Variable Rate Due 2038 \| Genco
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2038
Tax Exempt Financings 3.625% and 4.00% Due 2028 and 2033 \| Minimum [Member] \| DESC
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2028
Debt instrument, interest rate	3.625%
Tax Exempt Financings 3.625% and 4.00% Due 2028 and 2033 \| Maximum [Member] \| DESC
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2033
Debt instrument, interest rate	4.00%
3.05% Affiliated Note Due 2024 \| Genco
Debt Instrument [Line Items]
Debt Instrument, Maturity Year	2024
Debt instrument, interest rate	3.05%