Income Taxes - Schedule of Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal	$ 272.1	$ 126.6	$ 103.0
State	21.4	39.0	18.8
Foreign	168.5	86.8	19.4
Total current	462.0	252.4	141.2
Deferred	(1,781.8)	33.4	(7.2)
Total income tax provision (benefit)	(1,319.8)	285.8	134.0
Total provision (benefit) - discontinued operations		(0.2)	55.8
Total provision (benefit) - continuing operations	$ (1,319.8)	$ 286.0	$ 78.2