Taxation (Summary of (Provision) Benefit for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal	$ (38.8)	$ (147.5)	$ (161.0)
State	(20.5)	(30.2)	(18.9)
Foreign	(158.2)	(142.2)	(143.0)
Current income tax (provision)	(217.5)	(319.9)	(322.9)
Federal	(35.5)	63.0	(21.1)
State	(10.0)	(11.2)	(0.9)
Foreign	8.0	(0.1)	6.6
Deferred income tax (provision)	(37.5)	51.7	(15.4)
Total income tax (provision)	$ (255.0)	$ (268.2)	$ (338.3)