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Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	$ 52.3	$ 13.0
Current period provisions	54.6
Write-offs charged against allowance	(29.7)
Recoveries of amounts previously written off	14.4
Gas Distribution Operations
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	41.8	9.1
Current period provisions	45.3
Write-offs charged against allowance	(26.7)
Recoveries of amounts previously written off	14.1
Electric Operations
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	9.7	3.1
Current period provisions	9.3
Write-offs charged against allowance	(3.0)
Recoveries of amounts previously written off	0.3
Corporate and Other
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	0.8	$ 0.8
Current period provisions	0.0
Write-offs charged against allowance	0.0
Recoveries of amounts previously written off	$ 0.0

X

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

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