Employee Benefits (Net Periodic Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net periodic benefit cost:
Service cost	$ 5.4	$ 6.5	$ 4.6
Interest cost	51.1	55.9	57.2
Expected return on plan assets	(59.3)	(56.2)	(59.9)
Amortization of prior net loss	15.5	13.7	16.0
Settlement loss	7.6	0.0	28.7
Net periodic pension cost	20.3	19.9	46.6
Other changes in plan assets and benefit obligations recognized in other comprehensive loss (income):
Net actuarial gains (losses) and other adjustments	(43.7)	69.5	(52.0)
Net prior service credit	(10.7)	0.0	0.0
Settlement adjustment	(7.6)	0.0	(28.7)
Amortization of prior net losses	(15.5)	(13.7)	(16.0)
Total recognized in other comprehensive loss (income)	(77.5)	55.8	(96.7)
Total recognized in net periodic benefit cost and other comprehensive loss (income)	(57.2)	$ 75.7	(50.1)
Income tax provision (benefit) related to amounts in other comprehensive income	$ 13.3		$ 12.2