Income Taxes - Statutory Rate Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statutory rate reconciliation of amount
Statutory federal income tax	$ 367.3	$ 322.6	$ 363.5
State income taxes net of federal tax benefit	108.0	94.3	109.7
PTCs, net	(200.1)	(168.2)	(107.6)
Federal excess deferred tax amortization	(36.7)	(37.6)	(36.9)
AFUDC - Equity	(12.6)	(12.4)	(6.2)
Other, net	(3.9)	5.9	0.4
Total income tax expense	$ 222.0	$ 204.6	$ 322.9
Statutory rate reconciliation of percent
Statutory federal income tax	21.00%	21.00%	21.00%
State income taxes net of federal tax benefit	6.20%	6.10%	6.30%
PTCs, net	(11.50%)	(10.90%)	(6.20%)
Federal excess deferred tax amortization	(2.10%)	(2.40%)	(2.10%)
AFUDC - Equity	(0.70%)	(0.80%)	(0.40%)
Other, net	(0.20%)	0.30%	0.00%
Total income tax expense	12.70%	13.30%	18.60%
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