Income Taxes - Statutory rate reconciliation (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Statutory federal income tax		$ 315.1	$ 299.9	$ 264.4
State income taxes net of federal tax benefit		96.1	90.5	80.4
Wind PTCs		(81.3)	(51.5)	(34.1)
Federal excess deferred tax amortization - Wisconsin unprotected		(77.9)	(57.6)	0.0
Federal excess deferred tax amortization		(37.3)	(36.7)	(34.9)
ITC restored		(4.6)	(3.5)	(4.8)
AFUDC - Equity		(3.8)	(4.4)	(3.0)
Excess tax benefits - stock options		(3.2)	(12.3)	(15.8)
Tax repairs		4.0	3.3	(122.8)
Other, net		(6.8)	0.2	(4.4)
Total income tax expense		$ 200.3	$ 227.9	$ 125.0
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Statutory federal income tax		21.00%	21.00%	21.00%
State income taxes net of federal tax benefit		6.40%	6.30%	6.40%
Wind PTCs		(5.40%)	(3.60%)	(2.70%)
Federal excess deferred tax amortization - Wisconsin unprotected		(5.20%)	(4.00%)	0.00%
Federal excess deferred tax amortization		(2.50%)	(2.60%)	(2.80%)
ITC restored		(0.30%)	(0.20%)	(0.40%)
AFUDC - Equity		(0.30%)	(0.30%)	(0.20%)
Excess tax benefits - stock options		(0.20%)	(0.90%)	(1.30%)
Tax repairs		0.30%	0.20%	(9.80%)
Other, net		(0.40%)	0.00%	(0.30%)
Total income tax expense		13.40%	15.90%	9.90%
2018 and 2019 rates | Public Service Commission of Wisconsin (PSCW) | Tax Cuts and Jobs Act of 2017
Income taxes
Income Statement Impact of amortizing protected tax benefits		$ 0.0	$ 0.0	$ 0.0
2018 and 2019 rates | Public Service Commission of Wisconsin (PSCW) | WE | Tax Repairs Regulatory Asset
Income taxes
Income statement impact of flow through of repair related deferred tax liabilities				$ 0.0
2020 and 2021 rates | Public Service Commission of Wisconsin (PSCW) | Tax Cuts and Jobs Act of 2017
Income taxes
Income Statement Impact of amortizing unprotected tax benefits		$ 0.0	$ 0.0
2020 and 2021 rates | Public Service Commission of Wisconsin (PSCW) | WE | Tax Repairs Regulatory Asset
Income taxes
Amortization period		50 years
2020 and 2021 rates | Public Service Commission of Wisconsin (PSCW) | Electric rates | Tax Cuts and Jobs Act of 2017
Income taxes
Amortization period	2 years
2020 and 2021 rates | Public Service Commission of Wisconsin (PSCW) | Natural gas rates | Tax Cuts and Jobs Act of 2017
Income taxes
Amortization period	4 years