Goodwill and Other Intangible Assets - Goodwill (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Aug. 31, 2015	Jun. 30, 2015	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Roll Forward]
Balance at the beginning of the period, gross goodwill			$ 441.9	$ 441.9
Balance at the beginning of the period, accumulated impairment losses			0.0	0.0
Balance at the beginning of the period, net goodwill			441.9
Goodwill		$ 2,581.6	2,581.6	0.0
Balance at the end of the period, gross goodwill			3,023.5	441.9
Balance at the end of the period, accumulated impairment losses			0.0	0.0
Balance at the end of the period, net goodwill			3,023.5	441.9
Goodwill, Impairment Loss	$ 0.0
Wisconsin
Goodwill [Roll Forward]
Balance at the beginning of the period, gross goodwill			441.9	441.9
Balance at the beginning of the period, accumulated impairment losses			0.0	0.0
Balance at the beginning of the period, net goodwill			441.9	441.9
Goodwill			1,667.6	0.0
Balance at the end of the period, gross goodwill			2,109.5	441.9
Balance at the end of the period, accumulated impairment losses			0.0	0.0
Balance at the end of the period, net goodwill			2,109.5	441.9
Illinois
Goodwill [Roll Forward]
Balance at the beginning of the period, gross goodwill			0.0	0.0
Balance at the beginning of the period, accumulated impairment losses			0.0	0.0
Balance at the beginning of the period, net goodwill			0.0	0.0
Goodwill			731.2	0.0
Balance at the end of the period, gross goodwill			731.2	0.0
Balance at the end of the period, accumulated impairment losses			0.0	0.0
Balance at the end of the period, net goodwill			731.2	0.0
Other States
Goodwill [Roll Forward]
Balance at the beginning of the period, gross goodwill			0.0	0.0
Balance at the beginning of the period, accumulated impairment losses			0.0	0.0
Balance at the beginning of the period, net goodwill			0.0	0.0
Goodwill			182.8	0.0
Balance at the end of the period, gross goodwill			182.8	0.0
Balance at the end of the period, accumulated impairment losses			0.0	0.0
Balance at the end of the period, net goodwill			$ 182.8	$ 0.0