Segment Information (Details) $ in Millions	1 Months Ended		3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($)	Oct. 31, 2020 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment information
Number of reportable segments | segment											6
Operating revenues			$ 1,933.4	$ 1,651.0	$ 1,548.7	$ 2,108.6	$ 1,947.5	$ 1,608.0	$ 1,590.2	$ 2,377.4	$ 7,241.7	$ 7,523.1	$ 7,679.5
Other operation and maintenance											2,032.2	2,184.8	2,270.5
Depreciation and amortization											975.9	926.3	845.8
Equity in earnings of transmission affiliates											175.8	127.6	136.7
Interest expense											493.7	501.5	445.1
Loss on debt extinguishment	$ 10.5	$ 27.9									38.4	0.0	0.0
Income tax expense (benefit)											227.9	125.0	169.8
Net income (loss)											1,201.4	1,134.7	1,060.5
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
Capital expenditures and asset acquisitions											2,874.3	2,529.0	2,417.1
Total assets	37,028.1		37,028.1				34,951.8				37,028.1	34,951.8	33,475.8
Reconciling eliminations
Segment information
Other operation and maintenance											(9.2)	0.2	(393.3)
Depreciation and amortization											(52.8)	(15.8)	0.0
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											(345.5)	(354.1)	(5.3)
Loss on debt extinguishment											0.0
Income tax expense (benefit)											0.0	0.0	0.0
Net income (loss)											0.0	0.0	0.0
Net income attributed to common shareholders											0.0	0.0	0.0
Capital expenditures and asset acquisitions											0.0	0.0	0.0
Total assets	(3,361.2)		(3,361.2)				(3,344.5)				(3,361.2)	(3,344.5)	(3,414.5)
WE | Reconciling eliminations
Segment information
Total assets	1,824.5		1,824.5				1,896.7				1,824.5	1,896.7	1,968.5
Wisconsin
Segment information
Operating revenues											5,473.5	5,647.1	5,794.7
Illinois
Segment information
Operating revenues											1,321.9	1,357.1	1,400.0
Other States
Segment information
Operating revenues											384.1	426.0	438.2
Electric transmission
Segment information
Other operation and maintenance											0.0	0.0	0.0
Depreciation and amortization											0.0	0.0	0.0
Equity in earnings of transmission affiliates											175.8	127.6	136.7
Interest expense											19.4	13.1	0.3
Loss on debt extinguishment											0.0
Income tax expense (benefit)											43.7	27.1	53.7
Net income (loss)											112.6	87.4	82.8
Net income attributed to common shareholders											112.6	87.4	82.8
Capital expenditures and asset acquisitions											0.0	0.0	0.0
Total assets	1,764.7		1,764.7				1,723.1				$ 1,764.7	1,723.1	1,665.3
Non-Utility Energy Infrastructure
Segment information
Natural gas storage needs provided to Wisconsin utilities											33.00%
Operating revenues											$ 508.5	495.9	468.4
Other operation and maintenance											24.9	19.7	12.6
Depreciation and amortization											98.9	92.0	75.7
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											60.8	62.1	63.7
Loss on debt extinguishment											0.0
Income tax expense (benefit)											44.7	59.9	73.9
Net income (loss)											261.1	245.5	228.4
Net income attributed to common shareholders											260.8	246.0	228.4
Capital expenditures and asset acquisitions											661.8	389.9	260.6
Total assets	4,455.2		4,455.2				3,654.1				4,455.2	3,654.1	3,227.2
Corporate and other
Segment information
Operating revenues											2.2	4.4	8.7
Other operation and maintenance											17.4	14.0	1.8
Depreciation and amortization											25.1	24.3	29.1
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											124.0	140.9	125.8
Loss on debt extinguishment											38.4
Income tax expense (benefit)											(72.4)	(71.0)	(72.2)
Net income (loss)											(106.4)	(62.8)	(60.1)
Net income attributed to common shareholders											(106.4)	(62.8)	(60.1)
Capital expenditures and asset acquisitions											33.1	26.5	39.7
Total assets	$ 762.2		$ 762.2				814.0				$ 762.2	814.0	959.6
Bishop Hill III | Non-Utility Energy Infrastructure
Segment information
WEC's ownership interest	90.00%		90.00%								90.00%
Coyote Ridge | Non-Utility Energy Infrastructure
Segment information
WEC's ownership interest	80.00%		80.00%								80.00%
Upstream | Non-Utility Energy Infrastructure
Segment information
WEC's ownership interest	90.00%		90.00%								90.00%
Blooming Grove | Non-Utility Energy Infrastructure
Segment information
WEC's ownership interest	90.00%		90.00%								90.00%
Tatanka Ridge | Non-Utility Energy Infrastructure
Segment information
WEC's ownership interest	85.00%		85.00%								85.00%
ATC
Segment information
Equity method investment, ownership interest (as a percent)	60.00%		60.00%								60.00%
Operating revenues											$ 758.1	744.4	690.5
Equity in earnings of transmission affiliates											174.3	132.8	139.6
Total assets	$ 5,493.3		$ 5,493.3				5,328.9				$ 5,493.3	5,328.9
ATC | Electric transmission
Segment information
Equity method investment, ownership interest (as a percent)	60.00%		60.00%								60.00%
ATC Holdco
Segment information
Equity method investment, ownership interest (as a percent)	75.00%		75.00%								75.00%
Equity in earnings of transmission affiliates											$ 1.5	(5.2)	(2.9)
ATC Holdco | Electric transmission
Segment information
Equity method investment, ownership interest (as a percent)	75.00%		75.00%								75.00%
Public Utilities
Segment information
Other operation and maintenance											$ 1,999.1	2,150.9	2,649.4
Depreciation and amortization											904.7	825.8	741.0
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											635.0	639.5	260.6
Loss on debt extinguishment											0.0
Income tax expense (benefit)											211.9	109.0	114.4
Net income (loss)											934.1	864.6	809.4
Net income attributed to common shareholders											932.9	863.4	808.2
Capital expenditures and asset acquisitions											2,179.4	2,112.6	2,116.8
Total assets	$ 33,407.2		$ 33,407.2				32,105.1				33,407.2	32,105.1	31,038.2
Public Utilities | Wisconsin
Segment information
Other operation and maintenance											1,476.7	1,591.3	2,076.1
Depreciation and amortization											674.5	617.0	546.6
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											561.3	572.0	200.7
Loss on debt extinguishment											0.0
Income tax expense (benefit)											132.7	35.2	46.7
Net income (loss)											691.6	651.1	618.2
Net income attributed to common shareholders											690.4	649.9	617.0
Capital expenditures and asset acquisitions											1,382.4	1,378.6	1,466.1
Total assets	24,599.2		24,599.2				23,934.8				24,599.2	23,934.8	23,407.0
Public Utilities | Illinois
Segment information
Other operation and maintenance											435.4	461.1	472.3
Depreciation and amortization											196.7	181.3	170.3
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											63.5	59.0	51.2
Loss on debt extinguishment											0.0
Income tax expense (benefit)											66.1	60.2	51.8
Net income (loss)											203.5	170.3	147.1
Net income attributed to common shareholders											203.5	170.3	147.1
Capital expenditures and asset acquisitions											652.7	624.9	547.1
Total assets	7,471.8		7,471.8				6,932.5				7,471.8	6,932.5	6,483.3
Public Utilities | Other States
Segment information
Other operation and maintenance											87.0	98.5	101.0
Depreciation and amortization											33.5	27.5	24.1
Equity in earnings of transmission affiliates											0.0	0.0	0.0
Interest expense											10.2	8.5	8.7
Loss on debt extinguishment											0.0
Income tax expense (benefit)											13.1	13.6	15.9
Net income (loss)											39.0	43.2	44.1
Net income attributed to common shareholders											39.0	43.2	44.1
Capital expenditures and asset acquisitions											144.3	109.1	103.6
Total assets	$ 1,336.2		$ 1,336.2				$ 1,237.8				1,336.2	1,237.8	1,147.9
External Revenues | Reconciling eliminations
Segment information
Operating revenues											0.0	0.0	0.0
External Revenues | Electric transmission
Segment information
Operating revenues											0.0	0.0	0.0
External Revenues | Non-Utility Energy Infrastructure
Segment information
Operating revenues											60.0	88.5	37.9
External Revenues | Corporate and other
Segment information
Operating revenues											2.2	4.4	8.7
External Revenues | Public Utilities
Segment information
Operating revenues											7,179.5	7,430.2	7,632.9
External Revenues | Public Utilities | Wisconsin
Segment information
Operating revenues											5,473.5	5,647.1	5,794.7
External Revenues | Public Utilities | Illinois
Segment information
Operating revenues											1,321.9	1,357.1	1,400.0
External Revenues | Public Utilities | Other States
Segment information
Operating revenues											384.1	426.0	438.2
Intersegment Transactions
Segment information
Operating revenues											0.0	0.0	0.0
Intersegment Transactions | Reconciling eliminations
Segment information
Operating revenues											(448.5)	(407.4)	(430.5)
Intersegment Transactions | Electric transmission
Segment information
Operating revenues											0.0	0.0	0.0
Intersegment Transactions | Non-Utility Energy Infrastructure
Segment information
Operating revenues											448.5	407.4	430.5
Intersegment Transactions | Corporate and other
Segment information
Operating revenues											0.0	0.0	0.0
Intersegment Transactions | Public Utilities
Segment information
Operating revenues											0.0	0.0	0.0
Intersegment Transactions | Public Utilities | Wisconsin
Segment information
Operating revenues											0.0	0.0	0.0
Intersegment Transactions | Public Utilities | Illinois
Segment information
Operating revenues											0.0	0.0	0.0
Intersegment Transactions | Public Utilities | Other States
Segment information
Operating revenues											$ 0.0	$ 0.0	$ 0.0