Affiliated and Related Party Transactions (Schedule of Affiliated Transactions - Balance Sheet) (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
DESS [Member]
Related Party Transaction [Line Items]
Payable to affiliates	$ 59	$ 76
Public Service Company of North Carolina, Incorporated [Member]
Related Party Transaction [Line Items]
Payable to affiliates	5	8
Canadys Refined Coal [Member]
Related Party Transaction [Line Items]
Receivable from affiliates	0	2
Payable to affiliates	0	2
Solar Affiliates [Member]
Related Party Transaction [Line Items]
Payable to affiliates	1	0
DECG [Member]
Related Party Transaction [Line Items]
Receivable from affiliates	0	1
Payable to affiliates	$ 0	$ 5

Amount of receivables due from an entity that is affiliated with the reporting entity by means of direct or indirect ownership, due within 1 year (or 1 business cycle).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=120604989&loc=d3e56071-112765

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3(a)(2))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39599-107864

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Name:	us-gaap_DueFromAffiliateCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant