Income Taxes - Table 1 (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal									$ 2.6	$ 2.5	$ 0.9
State and local									12.2	10.8	5.4
Total current expense									14.8	13.3	6.3
Deferred:
Federal									113.9	95.3	11.3
State and local									13.2	2.1	(4.9)
Total deferred expense									127.1	97.4	6.4
Total income tax expense related to continuing operations	$ 43.5	$ 35.9	$ 32.2	$ 30.3	$ 19.3	$ 22.1	$ 36.5	$ 32.8	$ 141.9	$ 110.7	$ 12.7