DERIVATIVE INSTRUMENTS - CASH FLOW HEDGES (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) number_of_interest_rate_swaps	Jun. 30, 2018 USD ($)
Derivative [Line Items]
Interest expense	$ 124.1	$ 108.5	$ 248.5	$ 215.2
WEC Energy Group | WEC 2007 Junior Notes due 2067
Derivative [Line Items]
Long-term debt outstanding	500.0		$ 500.0
WEC Energy Group | Interest rate swaps
Derivative [Line Items]
Number of interest rate swaps executed | number_of_interest_rate_swaps			2
Interest rate swap notional value	$ 250.0		$ 250.0
Interest rate swap fixed interest rate	4.9765%		4.9765%
Derivative losses recognized in other comprehensive loss	$ (3.2)	0.0	$ (4.8)	0.0
Net derivative gains reclassified from accumulated other comprehensive loss to interest expense	0.4	$ 0.5	0.8	$ 1.1
Amount to be reclassified from accumulated other comprehensive loss to interest expense	$ 0.3		$ 0.3