Credit Losses - Rollforward of Allowances (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at December 31, 2019	$ 140.0
Provision for credit losses	102.9
Provision for credit losses deferred for future recovery or refund	55.2
Write-offs charged against the allowance	(132.3)
Recovery of amounts previously written off	54.4
Balance at December 31, 2020	220.1
WPS Power Development, LLC Residential Solar Facilities
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Sale of PDL residential solar facilities	(0.1)
Public Utilities
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at December 31, 2019	139.9
Provision for credit losses	102.9
Provision for credit losses deferred for future recovery or refund	55.2
Write-offs charged against the allowance	(132.3)
Recovery of amounts previously written off	54.4
Sale of PDL residential solar facilities	0.0
Balance at December 31, 2020	220.1
Wisconsin | Public Utilities
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at December 31, 2019	59.9
Provision for credit losses	47.5
Provision for credit losses deferred for future recovery or refund	24.6
Write-offs charged against the allowance	(65.9)
Recovery of amounts previously written off	36.0
Sale of PDL residential solar facilities	0.0
Balance at December 31, 2020	102.1
Illinois | Public Utilities
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at December 31, 2019	75.9
Provision for credit losses	51.1
Provision for credit losses deferred for future recovery or refund	30.6
Write-offs charged against the allowance	(63.0)
Recovery of amounts previously written off	17.0
Sale of PDL residential solar facilities	0.0
Balance at December 31, 2020	111.6
Other States | Public Utilities
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at December 31, 2019	4.1
Provision for credit losses	4.3
Provision for credit losses deferred for future recovery or refund	0.0
Write-offs charged against the allowance	(3.4)
Recovery of amounts previously written off	1.4
Sale of PDL residential solar facilities	0.0
Balance at December 31, 2020	6.4
Corporate and Other
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at December 31, 2019	0.1
Provision for credit losses	0.0
Provision for credit losses deferred for future recovery or refund	0.0
Write-offs charged against the allowance	0.0
Recovery of amounts previously written off	0.0
Balance at December 31, 2020	0.0
Corporate and Other | WPS Power Development, LLC Residential Solar Facilities
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Sale of PDL residential solar facilities	$ (0.1)