Pension and Other Postretirement Benefits - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0.3	$ 0.4	$ 0.7	$ 0.8
Interest cost	2.9	3.4	5.7	6.9
Expected return on plan assets	(4.5)	(4.8)	(9.0)	(9.6)
Amortization of net actuarial (gains) losses	1.0	1.2	2.1	2.3
Settlements	0.0	0.0	0.0	0.3
Net periodic cost (income)	(0.3)	0.2	(0.5)	0.7
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.0
Interest cost	0.0	0.1	0.1	0.2
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of net actuarial (gains) losses	0.0	(0.6)	0.0	(0.7)
Settlements	0.0	0.0	0.0	0.0
Net periodic cost (income)	$ 0.0	$ (0.5)	$ 0.1	$ (0.5)