Employee Benefit Plans (Net Periodic Pension Costs Included in Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Before-Tax Amount
Accumulated other comprehensive loss, before tax, beginning of period	$ (336.6)	$ (341.5)
Prior service cost arising during the year, before tax	(3.3)	(8.3)
Net loss recognized due to settlement, before tax	0.5	0.3
Net actuarial (loss) gain arising during the year, before tax	(76.5)	4.2
Amortization of prior service cost, before tax	1.2	0.6
Amortization of net actuarial losses	10.0	8.1
Accumulated other comprehensive loss, before tax, end of period	(404.8)	(336.6)	$ (341.5)
Income Tax
Accumulated other comprehensive loss, tax, beginning of period	(87.6)	(88.2)
Prior service cost arising during the year, tax	(0.7)	(3.6)
Net loss recognized due to settlement, tax	0.1	0.1
Net actuarial (loss) gain arising during the year, tax	(13.6)	2.1
Amortization of prior service costs, tax	0.1	0.2
Amortization of net actuarial losses, tax	1.4	1.8
Accumulated other comprehensive loss, tax, end of period	(100.3)	(87.6)	(88.2)
After-Tax Amount
Accumulated other comprehensive loss, after tax, beginning of period	(249.0)	(253.3)
Prior service cost arising during the year	(2.6)	(4.7)	0.0
Net loss recognized due to settlement	0.4	0.2	0.4
Net gain recognized due to curtailment	(0.1)	0.0	(0.4)
Net actuarial (loss) gain arising during the year, after tax	(62.9)	2.1	(54.8)
Amortization of prior service costs, after tax	1.1	0.4	0.6
Amortization of net actuarial losses included in net periodic pension cost	8.6	6.3	7.3
Accumulated other comprehensive loss, after tax, end of period	$ (304.5)	$ (249.0)	$ (253.3)