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Long-Term Debt - Debt Outstanding, Issuances, and Redemptions (Details) $ in Millions	1 Months Ended							12 Months Ended
	Dec. 31, 2020 USD ($) number_of_interest_rate_swaps	Nov. 30, 2020 USD ($)	Oct. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Aug. 31, 2020 USD ($)	May 31, 2020 USD ($)	Apr. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) number_of_interest_rate_swaps	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 12, 2018 number_of_interest_rate_swaps
Long-term debt
Total	$ 12,529.2							$ 12,529.2	$ 11,922.5
Integrys acquisition fair value adjustment	8.4							8.4	14.3
Unamortized debt issuance costs	(65.2)							(65.2)	(52.9)
Unamortized discount, net and other	(21.9)							(21.9)	(25.6)
Long-term debt, including current portion	12,450.5							12,450.5	11,858.3
Current portion of long-term debt	(777.7)							(777.7)	(686.9)
Long-term debt	11,672.8							11,672.8	11,171.4
Finance lease obligation	63.4							63.4	45.9
Loss on debt extinguishment	10.5		$ 27.9					38.4	0.0	$ 0.0
Future maturities of long-term debt outstanding
2021	777.7							777.7
2022	83.3							83.3
2023	784.9							784.9
2024	613.7							613.7
2025	1,156.7							1,156.7
Thereafter	9,112.9							9,112.9
Total	$ 12,529.2							$ 12,529.2	$ 11,922.5
WE
Long-term debt
Weighted average interest rate	4.26%							4.26%	4.26%
Unsecured debt	$ 2,785.0							$ 2,785.0	$ 2,785.0
WPS
Long-term debt
Weighted average interest rate	4.04%							4.04%	4.04%
Senior notes	$ 1,625.0							$ 1,625.0	$ 1,625.0
WG
Long-term debt
Weighted average interest rate	3.65%							3.65%	3.65%
Unsecured debt	$ 640.0							$ 640.0	$ 640.0
Integrys
Long-term debt
Weighted average interest rate									4.17%
Senior notes	$ 0.0							$ 0.0	$ 250.0
Integrys \| 6.00% Integrys junior notes
Long-term debt
Weighted average interest rate	6.00%							6.00%	6.00%
Unsecured debt	$ 400.0							$ 400.0	$ 400.0
Interest rate	6.00%							6.00%
Basis points added to three-month LIBOR rate								3.22%
Integrys \| 4.17% Integrys senior notes
Long-term debt
Interest rate		4.17%
Redemption of unsecured debt		$ 250.0
PGL
Long-term debt
Weighted average interest rate	3.45%							3.45%	3.59%
Secured debt	$ 1,670.0							$ 1,670.0	$ 1,520.0
PGL \| 1.875% PGL series WW bonds
Long-term debt
Interest rate					1.875%
Redemption of secured debt					$ 50.0
PGL \| 1.98% PGL series JJJ bonds
Long-term debt
Interest rate		1.98%
Issuance of debt		$ 200.0
NSG
Long-term debt
Weighted average interest rate	3.81%							3.81%	3.81%
Secured debt	$ 132.0							$ 132.0	$ 132.0
MERC
Long-term debt
Weighted average interest rate	3.27%							3.27%	3.51%
Senior notes	$ 170.0							$ 170.0	$ 120.0
MERC \| 2.69% MERC senior notes
Long-term debt
Interest rate							2.69%
Issuance of debt							$ 50.0
MGU
Long-term debt
Weighted average interest rate	3.18%							3.18%	3.51%
Senior notes	$ 150.0							$ 150.0	$ 90.0
MGU \| 2.69% MGU senior notes
Long-term debt
Interest rate							2.69%
Issuance of debt							$ 60.0
UMERC
Long-term debt
Weighted average interest rate	3.26%							3.26%	3.26%
Senior notes	$ 160.0							$ 160.0	$ 160.0
Bluewater Gas Storage
Long-term debt
Weighted average interest rate	3.76%							3.76%	3.76%
Senior notes	$ 117.8							$ 117.8	$ 120.3
ATC Holding LLC
Long-term debt
Weighted average interest rate	4.05%							4.05%	4.05%
Senior notes	$ 475.0							$ 475.0	$ 475.0
We Power
Long-term debt
Weighted average interest rate	5.59%							5.59%	5.57%
Secured debt	$ 970.8							$ 970.8	$ 1,005.2
WECC
Long-term debt
Weighted average interest rate	6.94%							6.94%	6.94%
Unsecured debt	$ 50.0							$ 50.0	$ 50.0
WECI Wind Holding I
Long-term debt
Weighted average interest rate	2.75%							2.75%
Senior notes	$ 413.6							$ 413.6	$ 0.0
WECI Wind Holding I \| 2.75% WECI Wind Holding I senior notes
Long-term debt
Interest rate	2.75%							2.75%
Issuance of debt	$ 413.6
WEC Energy Group
Long-term debt
Weighted average interest rate	2.03%							2.03%	3.47%
Senior notes	$ 2,270.0							$ 2,270.0	$ 2,050.0
Current portion of long-term debt	0.0							0.0	(400.0)
Long-term debt	2,754.8							2,754.8	2,141.6
Loss on debt extinguishment								38.4	$ 0.0	$ 0.0
Future maturities of long-term debt outstanding
2021	0.0							0.0
2022	0.0							0.0
2023	700.0							700.0
2024	0.0							0.0
2025	420.0							420.0
Thereafter	$ 1,650.0							$ 1,650.0
WEC Energy Group \| WEC Energy Group junior notes due 2067
Long-term debt
Weighted average interest rate	3.65%							3.65%	4.50%
Unsecured debt	$ 500.0							$ 500.0	$ 500.0
Interest rate	2.33%							2.33%	4.02%
WEC Energy Group \| 6.20% WEC Energy Group senior notes
Long-term debt
Interest rate	6.20%							6.20%
WEC Energy Group \| 2.45% WEC Energy Group senior notes
Long-term debt
Interest rate						2.45%
Redemption of unsecured debt						$ 400.0
WEC Energy Group \| 0.55% WEC Energy Group senior notes
Long-term debt
Interest rate				0.55%
Issuance of debt				$ 700.0
WEC Energy Group \| 1.375% WEC Energy Group senior notes
Long-term debt
Interest rate			1.375%
Issuance of debt			$ 500.0
WEC Energy Group \| 1.800% WEC Energy Group senior notes
Long-term debt
Interest rate			1.80%
Issuance of debt			$ 450.0
WEC Energy Group \| 3.375% WEC Energy Group senior notes
Long-term debt
Interest rate			3.375%
Redemption of unsecured debt			$ 600.0
WEC Energy Group \| 3.10% WEC Energy Group senior notes
Long-term debt
Interest rate			3.10%
Redemption of unsecured debt			$ 350.0
WEC Energy Group \| 3.55% WEC Energy Group senior notes
Long-term debt
Senior notes	$ 500.0							$ 500.0
Interest rate	3.55%							3.55%
Redemption of unsecured debt	$ 80.0
WEC Energy Group \| Interest rate swaps
Long-term debt
Number of interest rate swaps executed \| number_of_interest_rate_swaps	2							2			2
Interest rate swap fixed interest rate	4.9765%							4.9765%
Interest rate swap notional value	$ 250.0							$ 250.0