SEGMENT INFORMATION (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) segment	Mar. 31, 2021 USD ($)
Segment information
Number of reportable segments | segment	6
Total operating revenues	$ 2,908.1	$ 2,691.4
Other operation and maintenance	454.4	479.9
Depreciation and amortization	278.1	261.4
Equity in earnings of transmission affiliates	41.7	42.6
Interest expense	117.6	119.5
Income tax expense (benefit)	127.1	74.9
Net income	568.0	510.3
Net income attributed to common shareholders	565.9	510.1
External Revenues
Segment information
Total operating revenues	2,908.1	2,691.4
Intersegment Revenues
Segment information
Total operating revenues	0.0	0.0
Utility Operations
Segment information
Other operation and maintenance	450.8	474.4
Depreciation and amortization	253.9	238.1
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	157.3	158.1
Income tax expense (benefit)	147.9	97.9
Net income	433.3	393.4
Net income attributed to common shareholders	433.0	393.1
Utility Operations | External Revenues
Segment information
Total operating revenues	2,865.3	2,668.4
Utility Operations | Intersegment Revenues
Segment information
Total operating revenues	0.0	0.0
Reconciling Eliminations
Segment information
Other operation and maintenance	(1.6)	(1.6)
Depreciation and amortization	(16.3)	(14.3)
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	(84.4)	(85.7)
Income tax expense (benefit)	0.0	0.0
Net income	0.0	0.0
Net income attributed to common shareholders	0.0	0.0
Reconciling Eliminations | External Revenues
Segment information
Total operating revenues	0.0	0.0
Reconciling Eliminations | Intersegment Revenues
Segment information
Total operating revenues	$ (116.9)	(114.7)
ATC Holdco
Segment information
Equity method investment, ownership interest (as a percent)	75.00%
Equity in earnings of transmission affiliates	$ 0.7	0.9
Wisconsin
Segment information
Total operating revenues	1,942.3	1,731.7
Wisconsin | Utility Operations
Segment information
Other operation and maintenance	312.6	341.9
Depreciation and amortization	187.1	176.2
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	136.3	140.1
Income tax expense (benefit)	95.4	48.1
Net income	288.4	256.6
Net income attributed to common shareholders	288.1	256.3
Wisconsin | Utility Operations | External Revenues
Segment information
Total operating revenues	1,942.3	1,731.7
Wisconsin | Utility Operations | Intersegment Revenues
Segment information
Total operating revenues	0.0	0.0
Illinois
Segment information
Total operating revenues	682.1	703.4
Illinois | Utility Operations
Segment information
Other operation and maintenance	113.6	109.3
Depreciation and amortization	56.8	52.7
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	17.7	16.5
Income tax expense (benefit)	42.1	41.4
Net income	113.4	112.1
Net income attributed to common shareholders	113.4	112.1
Illinois | Utility Operations | External Revenues
Segment information
Total operating revenues	682.1	703.4
Illinois | Utility Operations | Intersegment Revenues
Segment information
Total operating revenues	0.0	0.0
Other States
Segment information
Total operating revenues	240.9	233.3
Other States | Utility Operations
Segment information
Other operation and maintenance	24.6	23.2
Depreciation and amortization	10.0	9.2
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	3.3	1.5
Income tax expense (benefit)	10.4	8.4
Net income	31.5	24.7
Net income attributed to common shareholders	31.5	24.7
Other States | Utility Operations | External Revenues
Segment information
Total operating revenues	240.9	233.3
Other States | Utility Operations | Intersegment Revenues
Segment information
Total operating revenues	0.0	0.0
Electric Transmission
Segment information
Other operation and maintenance	0.0	0.0
Depreciation and amortization	0.0	0.0
Equity in earnings of transmission affiliates	41.7	42.6
Interest expense	4.9	4.9
Income tax expense (benefit)	8.9	9.8
Net income	27.8	28.0
Net income attributed to common shareholders	27.8	28.0
Electric Transmission | External Revenues
Segment information
Total operating revenues	0.0	0.0
Electric Transmission | Intersegment Revenues
Segment information
Total operating revenues	$ 0.0	0.0
Electric Transmission | ATC
Segment information
Equity method investment, ownership interest (as a percent)	60.00%
Electric Transmission | ATC Holdco
Segment information
Equity method investment, ownership interest (as a percent)	75.00%
Non-Utility Energy Infrastructure
Segment information
Natural gas storage needs provided to Wisconsin utilities	33.00%
Total operating revenues	$ 159.5	137.6
Other operation and maintenance	10.9	8.9
Depreciation and amortization	34.0	31.0
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	17.2	18.0
Income tax expense (benefit)	(4.9)	0.1
Net income	93.3	71.3
Net income attributed to common shareholders	91.5	71.4
Non-Utility Energy Infrastructure | External Revenues
Segment information
Total operating revenues	42.6	22.9
Non-Utility Energy Infrastructure | Intersegment Revenues
Segment information
Total operating revenues	$ 116.9	114.7
Non-Utility Energy Infrastructure | Bishop Hill III
Segment information
WEC's ownership interest	90.00%
Non-Utility Energy Infrastructure | Coyote Ridge
Segment information
WEC's ownership interest	80.00%
Non-Utility Energy Infrastructure | Upstream
Segment information
WEC's ownership interest	90.00%
Non-Utility Energy Infrastructure | Blooming Grove
Segment information
WEC's ownership interest	90.00%
Non-Utility Energy Infrastructure | Tatanka Ridge
Segment information
WEC's ownership interest	85.00%
Non-Utility Energy Infrastructure | Jayhawk
Segment information
WEC's ownership interest	90.00%
Corporate and Other
Segment information
Total operating revenues	$ 0.2	0.1
Other operation and maintenance	(5.7)	(1.8)
Depreciation and amortization	6.5	6.6
Equity in earnings of transmission affiliates	0.0	0.0
Interest expense	22.6	24.2
Income tax expense (benefit)	(24.8)	(32.9)
Net income	13.6	17.6
Net income attributed to common shareholders	13.6	17.6
Corporate and Other | External Revenues
Segment information
Total operating revenues	0.2	0.1
Corporate and Other | Intersegment Revenues
Segment information
Total operating revenues	$ 0.0	$ 0.0