Schedule I - Statements of Cash Flows (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended								12 Months Ended
	Dec. 31, 2020	Oct. 31, 2020	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Operating activities
Net income attributed to common shareholders			$ 239.0	$ 266.8	$ 241.6	$ 452.5	$ 243.9	$ 234.3	$ 235.7	$ 420.1	$ 1,199.9	$ 1,134.0	$ 1,059.3
Reconciliation to cash provided by operating activities
Equity income in subsidiaries, net of distributions											(29.1)	(2.9)	(18.6)
Deferred income taxes											182.2	167.7	300.1
Loss on debt extinguishment	$ 10.5	$ 27.9									38.4	0.0	0.0
Change in -
Other current liabilities											(41.2)	78.7	(67.6)
Other, net											3.4	20.6	290.4
Net cash provided by operating activities											2,196.0	2,345.5	2,445.5
Investing activities
Capital contributions to subsidiaries											(21.2)	(52.6)	(53.5)
Other, net											(5.3)	16.5	20.5
Net cash used in investing activities											(2,806.8)	(2,494.9)	(2,384.4)
Financing activities
Exercise of stock options											43.8	67.0	29.1
Purchase of common stock											(99.2)	(140.1)	(72.4)
Dividends paid on common stock											(798.0)	(744.5)	(697.3)
Issuance of long-term debt											2,373.6	1,895.0	1,740.0
Retirement of long-term debt											(1,767.0)	(360.1)	(953.3)
Issuance of short-term loan											340.0	0.0	0.0
Payments for debt extinguishment and issuance costs											(55.8)	(12.5)	(9.5)
Other, net											(11.4)	(9.9)	(5.7)
Net cash used in financing activities											(601.1)	(85.6)	(26.4)
Cash and cash equivalents at beginning of year						37.5				84.5	37.5	84.5
Cash and cash equivalents at end of year	24.8		24.8				37.5				24.8	37.5	84.5
WEC Energy Group
Operating activities
Net income attributed to common shareholders											1,199.9	1,134.0	1,059.3
Reconciliation to cash provided by operating activities
Equity income in subsidiaries, net of distributions											(385.7)	(475.2)	(419.4)
Deferred income taxes											12.7	9.1	14.4
Loss on debt extinguishment											38.4	0.0	0.0
Change in -
Accounts receivable from related parties											0.0	3.3	(2.1)
Prepaid taxes											(7.9)	(46.5)	17.5
Accounts payable to related parties											29.2	(5.2)	4.6
Other current liabilities											(2.4)	1.5	4.7
Other, net											9.6	7.0	5.6
Net cash provided by operating activities											893.8	628.0	684.6
Investing activities
Capital contributions to subsidiaries											(1,026.1)	(602.3)	(448.7)
Return of capital from subsidiaries											602.8	337.3	290.2
Short-term notes receivable from related parties, net											(88.3)	48.5	(6.9)
Issuance of long-term notes receivable from UMERC											0.0	0.0	(100.0)
Redemption of long-term notes receivable from UMERC											0.0	150.0	0.0
Other, net											3.7	(0.6)	6.4
Net cash used in investing activities											(507.9)	(67.1)	(259.0)
Financing activities
Exercise of stock options											43.8	67.0	29.1
Purchase of common stock											(99.2)	(140.1)	(72.4)
Dividends paid on common stock											(798.0)	(744.5)	(697.3)
Issuance of long-term debt											1,650.0	350.0	600.0
Retirement of long-term debt											(1,430.0)	0.0	(300.0)
Issuance of short-term loan											340.0	0.0	0.0
Change in other short-term debt											145.7	(213.7)	53.6
Short-term notes payable to related parties, net											(186.3)	90.4	(6.2)
Payments for debt extinguishment and issuance costs											(47.3)	(0.8)	(1.2)
Other, net											(1.1)	(1.5)	(2.4)
Net cash used in financing activities											382.4	593.2	396.8
Net change in cash and cash equivalents											3.5	(32.3)	28.8
Cash and cash equivalents at beginning of year						$ 0.5				$ 32.8	0.5	32.8	4.0
Cash and cash equivalents at end of year	$ 4.0		$ 4.0				$ 0.5				$ 4.0	$ 0.5	$ 32.8