Schedule I - Statements of Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statements of comprehensive income
Net income attributed to common shareholders	$ 205.0	$ 233.2	$ 231.0	$ 390.1	$ 432.6	$ 215.4	$ 199.1	$ 356.6	$ 1,059.3	$ 1,203.7	$ 939.0
Other comprehensive loss, net of tax									(5.5)	0.0	(1.7)
Comprehensive income attributed to common shareholders									1,053.8	1,203.7	937.3
Cash flow hedges
Other comprehensive (loss) income, net of tax
Cumulative effect adjustment from adoption of ASU 2018-02	1.6				0.0				1.6	0.0	0.0
Derivatives accounted for as cash flow hedges
Net derivative losses, net of tax									(2.1)	0.0	0.0
Reclassification of net gains to net income, net of tax									(1.2)	(1.3)	(1.3)
Cash flow hedges, net									(1.7)	(1.3)	(1.3)
Defined benefit plans
Other comprehensive (loss) income, net of tax
Cumulative effect adjustment from adoption of ASU 2018-02	(1.0)				0.0				(1.0)	0.0	0.0
Defined benefit plans
Pension and OPEB costs arising during the period, net of tax									(3.1)	0.9	(0.8)
Amortization of pension and OPEB costs included in net periodic benefit cost, net of tax									0.3	0.4	0.4
Defined benefit plans, net									(3.8)	1.3	(0.4)
WEC Energy Group
Statements of comprehensive income
Net income attributed to common shareholders									1,059.3	1,203.7	939.0
Other comprehensive (loss) income from subsidiaries, net of tax									(2.8)	1.2	0.3
Other comprehensive loss, net of tax									(5.5)	0.0	(1.7)
Comprehensive income attributed to common shareholders									1,053.8	1,203.7	937.3
WEC Energy Group | Cash flow hedges
Other comprehensive (loss) income, net of tax
Cumulative effect adjustment from adoption of ASU 2018-02	1.6				0.0				1.6	0.0	0.0
Derivatives accounted for as cash flow hedges
Net derivative losses, net of tax									(2.1)	0.0	0.0
Reclassification of net gains to net income, net of tax									(1.2)	(1.3)	(1.3)
Cash flow hedges, net									(1.7)	(1.3)	(1.3)
WEC Energy Group | Defined benefit plans
Other comprehensive (loss) income, net of tax
Cumulative effect adjustment from adoption of ASU 2018-02	$ (0.3)				$ 0.0				(0.3)	0.0	0.0
Defined benefit plans
Pension and OPEB costs arising during the period, net of tax									(0.9)	(0.1)	(1.0)
Amortization of pension and OPEB costs included in net periodic benefit cost, net of tax									0.2	0.2	0.3
Defined benefit plans, net									$ (1.0)	$ 0.1	$ (0.7)