Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Changes in Unrecognized Tax Benefits
Beginning balance, Unrecognized tax benefits		$ 42.1	$ 194.1
Additions based on tax positions related to the current year		23.2	0.8
Additions for tax positions of prior years			43.7
Reductions for tax positions related to the current year		(2.2)	(10.6)
Reductions for tax positions of prior years		(0.5)	(23.2)
Settlements			(162.7)
Ending balance, Unrecognized tax benefits	$ 62.6	$ 62.6	$ 42.1
Foreign undistributed earnings previously indefinitely reinvested that were repatriated	$ 250.0