Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of period	$ 90.3	$ 128.3	$ 112.2
Additions based upon prior year tax positions (including acquired uncertain tax positions)	2.7	4.0	1.7
Additions based on current year tax positions	3.1	6.5	76.2
Reductions for prior period positions	(6.9)	(38.0)	(51.9)
Reductions for settlements and payments	(4.3)	(4.2)	0.0
Reductions due to closed statutes	(3.5)	(6.3)	(9.9)
Total unrecognized tax benefits at end of period	$ 81.4	$ 90.3	$ 128.3