v3.20.1

Derivative Instruments - Notional Amount of Derivative Instruments (Details) $ in Billions		3 Months Ended	12 Months Ended
		Mar. 31, 2020 USD ($) MMBTU MWh t	Dec. 31, 2019 USD ($) MMBTU MWh t
Derivative [Line Items]
Derivative, amount of hedged item	[1]	$ 1.6
Power
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MWh		190	184
Natural Gas Contracts
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU		913	1,063
Environmental credits
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Mass | t		37	26
Interest rate hedging instruments
Derivative [Line Items]
Derivative, notional amount	[1]	$ 6.6	$ 4.8
[1] (1)During the first quarter of 2020, we entered into interest rate hedging instruments to hedge approximately $1.6 billion of variable rate debt.

X

- Definition

Amount of hedged item in hedging relationship. Excludes hedged asset or liability.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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X

- 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

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Data Type:	xbrli:stringItemType
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X

- Definition

Nominal energy measure used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Nominal mass used to calculate payments on a derivative instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:massItemType
Balance Type:	na
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X

- 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=109980867&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=109980867&loc=SL5579245-113959

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X

- Details

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X

- Details

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X

- Details

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X

- Details

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