Risk Management and Hedging Activities - PAC - Derivative Contract Volumes (Details) - PAC - Commodity derivatives MWh in Millions, Dth in Millions	Sep. 30, 2021 MWh Dth	Dec. 31, 2020 Dth MWh
Electricity sales, net
Notional Amounts of Outstanding Derivative Positions [Line Items]
Nonmonetary notional amount \| MWh	0	(1)
Natural gas purchases
Notional Amounts of Outstanding Derivative Positions [Line Items]
Nonmonetary notional amount \| Dth	101	100

Nominal number of units used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 40
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123477628&loc=d3e90205-114008

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5580258-113959

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 18
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123467817&loc=SL123496189-112644

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=125515794&loc=SL5579245-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant