Income Taxes Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 20.2	$ 20.3	$ 21.6
Additions based on tax positions relating to the current year	13.6	2.8	2.9
Reductions based on expiration of statute of limitations	(1.4)	(5.7)	(2.8)
Additions to tax positions relating to previous years	1.0	2.9	0.4
Settlements	(3.9)	(0.1)	(1.8)
TOTAL UNRECOGNIZED TAX BENEFITS	$ 29.5	$ 20.2	$ 20.3