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Variable Interest Entities (Narrative) (Details)	3 Months Ended		4 Months Ended
	Mar. 31, 2021 USD ($) Rate MW	Mar. 31, 2020 USD ($)	Mar. 31, 2021 USD ($) Rate MW	Dec. 31, 2020 USD ($)
Variable Interest Entity [Line Items]
Nameplate Capacity | MW	102		102
Wind Power Purchase Agreement, Purchase Percentage | Rate	100.00%		100.00%
Total Equity Membership Interest	100.00%		100.00%
Additional Obligation to the Developer	$ 6,000,000.0		$ 6,000,000.0
Payment to renewable generation asset developer	(7,400,000)	$ 0
Total Obligation to the Developer	75,700,000		75,700,000
Total Contributions	170,100,000		170,100,000
VIE Net Assets	170,000,000.0		170,000,000.0	$ 156,400,000
Noncontrolling interest in consolidated subsidiaries	94,100,000		$ 94,100,000	$ 85,600,000
Net income attributable to noncontrolling interest	$ 1,000,000.0	$ 0
Rosewater Wind Farm
Variable Interest Entity [Line Items]
Wind Power Purchase Agreement, Purchase Percentage | Rate	100.00%		100.00%
NIPSCO
Variable Interest Entity [Line Items]
Cash Contribution	$ 100,000		$ 800,000
Tax Equity Partner
Variable Interest Entity [Line Items]
Cash Contribution	$ 7,500,000		$ 93,600,000

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