Employee Benefits (Other Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net prior service credit	$ (10.7)	$ 0.0	$ 0.0
Amortization of prior net loss	15.5	13.7	16.0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax	(77.5)	55.8	(96.7)
Settlement loss	$ (7.6)	$ 0.0	(28.7)
Discount rate, benefit obligations	3.77%	4.27%
Noncash equity-based compensation and employee benefits expense	$ 22.0	$ 21.0	24.4
Management
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Noncash equity-based compensation and employee benefits expense	1.8	2.1	14.1
Performance Incentive Awards
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Performance and sales incentive expense	$ 11.6	$ 11.7	$ 13.2