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Long-Term Debt and Capital Lease Obligations - Long-term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	May 15, 2017	Dec. 31, 2016	Aug. 01, 2016
Future maturities of long-term debt outstanding
2018	$ 838.4
2019	360.1
2020	686.9
2021	338.8
2022	40.7
Thereafter	7,336.0
Total	$ 9,600.9
WEC Energy Group junior notes (unsecured), 3.53% due 2067
Debt Disclosure [Abstract]
Debt instrument, basis spread on variable rate	2.1125%
Debt instrument interest rate stated percentage rate	3.53%	6.25%
WEC Energy Group
Debt Disclosure [Abstract]
Current portion of long-term debt	$ 300.0		$ 0.0
Future maturities of long-term debt outstanding
2018	300.0
2020	400.0
Thereafter	1,200.0
Total	1,900.0
WEC Energy Group \| WEC Energy Group senior notes (unsecured), 6.20% due 2033
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 200.0		200.0
Debt instrument interest rate stated percentage rate	6.20%
WEC Energy Group \| WEC Energy Group junior notes (unsecured), 3.53% due 2067
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 500.0		500.0
Debt instrument interest rate stated percentage rate	3.53%
WPS \| WPS senior notes 5.65% matured November 2017
Debt Disclosure [Abstract]
Repayments of debt	$ 125.0
Debt instrument interest rate stated percentage rate	5.65%
PGL \| PGL first and refunding mortgage bonds (secured), 3.77% due 2047
Debt Disclosure [Abstract]
Debt instrument interest rate stated percentage rate	3.77%
Proceeds from issuance of debt	$ 100.0
We Power \| We Power Notes (secured, nonrecourse), 4.91% due 2015-2030
Debt Disclosure [Abstract]
Debt instrument interest rate stated percentage rate	4.91%
Current portion of long-term debt	$ 5.9
Long-term debt, gross	$ 101.0
We Power \| We Power Notes (secured, nonrecourse), 6.00% due 2015-2033
Debt Disclosure [Abstract]
Debt instrument interest rate stated percentage rate	6.00%
Current portion of long-term debt	$ 4.9
Long-term debt, gross	$ 121.5
We Power \| We Power Notes (secured, nonrecourse), 5.209% due 2015-2030
Debt Disclosure [Abstract]
Debt instrument interest rate stated percentage rate	5.209%
Current portion of long-term debt	$ 11.4
Long-term debt, gross	$ 194.1
We Power \| We Power Notes (secured, nonrecourse), 4.673% due 2015-2031
Debt Disclosure [Abstract]
Debt instrument interest rate stated percentage rate	4.673%
Current portion of long-term debt	$ 8.9
Long-term debt, gross	162.4
Integrys Holding Inc \| Integrys senior notes (unsecured), 4.17% due 2020
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 250.0		250.0
Debt instrument interest rate stated percentage rate	4.17%
Integrys Holding Inc \| Integrys junior notes (unsecured), 6.00% due 2073
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 400.0		400.0
Debt instrument, basis spread on variable rate	3.22%
Debt instrument interest rate stated percentage rate	6.00%
Long-term debt, gross	$ 400.0
MERC
Debt Disclosure [Abstract]
Proceeds from issuance of debt	120.0
MERC \| MERC senior notes (unsecured), 3.11% due 2027
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 40.0		0.0
Debt instrument interest rate stated percentage rate	3.11%
Proceeds from issuance of debt	$ 40.0
MERC \| MERC senior notes (unsecured), 3.41% due 2032
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 40.0		0.0
Debt instrument interest rate stated percentage rate	3.41%
Proceeds from issuance of debt	$ 40.0
MERC \| MERC senior notes (unsecured), 4.01% due 2047
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 40.0		0.0
Debt instrument interest rate stated percentage rate	4.01%
Proceeds from issuance of debt	$ 40.0
MGU
Debt Disclosure [Abstract]
Proceeds from issuance of debt	90.0
MGU \| MGU senior notes (unsecured), 3.11% due 2027
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 30.0		0.0
Debt instrument interest rate stated percentage rate	3.11%
Proceeds from issuance of debt	$ 30.0
MGU \| MGU senior notes (unsecured), 3.41% due 2032
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 30.0		0.0
Debt instrument interest rate stated percentage rate	3.41%
Proceeds from issuance of debt	$ 30.0
MGU \| MGU senior notes (unsecured), 4.01% due 2047
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 30.0		0.0
Debt instrument interest rate stated percentage rate	4.01%
Proceeds from issuance of debt	$ 30.0
Bluewater Gas Storage, LLC \| Bluewater Gas Storage senior notes (unsecured), 3.76% due 2047
Debt Disclosure [Abstract]
Long-term debt, unsecured	$ 125.0		$ 0.0
Debt instrument interest rate stated percentage rate	3.76%
Proceeds from issuance of debt	$ 125.0
Current portion of long-term debt	2.3
Long-term debt, gross	125.0
WE
Debt Disclosure [Abstract]
Long-term pollution control bond	80.0			$ 67.0
Integrys Holding Inc \| MERC
Debt Disclosure [Abstract]
Repayments of debt	78.0
Integrys Holding Inc \| MGU
Debt Disclosure [Abstract]
Repayments of debt	$ 71.0