Income Taxes - Accounting for Uncertainty in Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance at January 1,	$ 129.9	$ 114.2	$ 66.8
Additions based on tax positions related to the current period	1.5	5.3	0.5
Additions for tax positions of prior periods	51.7	17.2	58.7
Reductions for tax positions of prior periods	(63.6)	(10.3)	(13.6)
Statute expirations	(7.9)	(0.1)	(2.9)
Settlement refund (payment)		3.6	4.7
Settlement refund (payment)	(35.9)
Ending balance ar December 31,	$ 75.7	$ 129.9	$ 114.2