Derivatives and Risk Management Activities - Interest Rate Risk Hedging (Details) - Cash Flow Hedging $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($) contract
8 forward starting interest rate swaps (30-year), 1.38%
Interest Rate Derivatives [Abstract]
Number of interest rate derivatives \| contract	8
Term of derivative contract	30 years
8 forward starting interest rate swaps (30-year), 0.73%
Interest Rate Derivatives [Abstract]
Number of interest rate derivatives \| contract	8
Term of derivative contract	30 years
Notional amount of derivatives \| $	$ 200
Average rate locked (percent)	0.73%
Eight Forward Starting Thirty Year Interest Rate Swaps 1.38 Percent
Interest Rate Derivatives [Abstract]
Notional amount of derivatives \| $	$ 200
Average rate locked (percent)	1.38%

Average fixed interest rate related to the group of interest rate derivatives.

No definition available.

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- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: 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=121590274&loc=SL5580258-113959

Reference 2: 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=121590274&loc=SL5579245-113959

+ Details

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- Definition

Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- References

No definition available.

+ Details

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- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

+ Details

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- Details

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