Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued [Abstract]
Balance at beginning of period	$ 246.7	$ 226.9	$ 238.0
Increases as a result of tax positions taken during a prior year	6.3	65.0	5.2
Decreases as a result of tax positions taken during a prior year	(8.1)	(47.5)	(19.7)
Settlements with taxing authorities	(0.8)	(4.6)	(4.1)
Lapse of statutes of limitation	(3.3)	(11.8)	(3.8)
Increases as a result of tax positions taken during the current year	31.1	18.7	11.3
Balance at end of period	271.9	246.7	$ 226.9
Income Tax Contingency [Line Items]
Unrecognized tax benefits that would impact effective tax rate	249.2
Income tax penalties and interest accrued	27.9	20.9
Income tax penalties and interest expense	7.0	$ 0.7
Minimum [Member]
Income Tax Contingency [Line Items]
Anticipated decrease in unrecognized tax benefits	28.0
Maximum [Member]
Income Tax Contingency [Line Items]
Anticipated decrease in unrecognized tax benefits	$ 38.0