Income Taxes (Details 3) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the beginning and ending of unrecognized tax benefits
Balance at January 1	$ 32.4	$ 67.9	$ 131.5
Additions based on tax positions related to the current period	5.7	7.2	10.5
Additions for tax positions of prior periods	7.3	36.3	19.5
Reductions for tax positions of prior periods	(21.8)	(13.3)	(49.9)
Statute expirations	(1.4)	(1.4)	(1.2)
Settlements	44.6	64.3	42.5
Balance at December 31	$ 66.8	$ 32.4	$ 67.9