Income Taxes - Statutory Rate Reconciliation (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statutory rate reconciliation of amount
Statutory federal income tax		$ 363.5	$ 315.1	$ 299.9
State income taxes net of federal tax benefit		109.7	96.1	90.5
Wind PTCs		(107.6)	(81.3)	(51.5)
Federal excess deferred tax amortization		(36.9)	(37.3)	(36.7)
AFUDC - Equity		(6.2)	(3.8)	(4.4)
ITC restored		(5.8)	(4.6)	(3.5)
Federal excess deferred tax amortization - Wisconsin unprotected		(0.8)	(77.9)	(57.6)
Other, net		7.0	(6.0)	(8.8)
Total income tax expense		$ 322.9	$ 200.3	$ 227.9
Statutory rate reconciliation of percent
Statutory federal income tax		21.00%	21.00%	21.00%
State income taxes net of federal tax benefit		6.30%	6.40%	6.30%
Wind PTCs		(6.20%)	(5.40%)	(3.60%)
Federal excess deferred tax amortization		(2.10%)	(2.50%)	(2.60%)
AFUDC - Equity		(0.40%)	(0.30%)	(0.30%)
ITC restored		(0.30%)	(0.30%)	(0.20%)
Federal excess deferred tax amortization - Wisconsin unprotected		0.00%	(5.20%)	(4.00%)
Other, net		0.30%	(0.30%)	(0.70%)
Total income tax expense		18.60%	13.40%	15.90%
Public Service Commission of Wisconsin (PSCW) | Tax Cuts and Jobs Act of 2017 | 2020 and 2021 rates
Income taxes
Income statement impact of amortizing unprotected tax benefits		$ 0.0	$ 0.0	$ 0.0
Public Service Commission of Wisconsin (PSCW) | Tax Cuts and Jobs Act of 2017 | 2020 and 2021 rates | Electric rates
Income taxes
Amortization period	2 years
Public Service Commission of Wisconsin (PSCW) | Tax Cuts and Jobs Act of 2017 | 2020 and 2021 rates | Natural gas rates
Income taxes
Amortization period	4 years
Public Service Commission of Wisconsin (PSCW) | Tax Cuts and Jobs Act of 2017 | 2018 and 2019 rates
Income taxes
Income statement impact of amortizing protected tax benefits		$ 0.0	$ 0.0	$ 0.0