Revenue Recognition Revenue Recognition (Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	$ 53.9	$ 52.3
Current period provisions	8.8
Write-offs charged against allowance	(11.4)
Recoveries of amounts previously written off	4.2
Gas Distribution Operations
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	42.8	41.8
Current period provisions	5.9
Write-offs charged against allowance	(9.0)
Recoveries of amounts previously written off	4.1
Electric Operations
Financing Receivable, Allowance for Credit Loss [Line Items]
Allowance for Credit Loss	10.3	9.7
Current period provisions	2.9
Write-offs charged against allowance	(2.4)
Recoveries of amounts previously written off	0.1
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

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

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