Employee Benefit Plans - Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (net of tax) [Abstract]
Amortization of unrecognized gain (loss)	$ (14.3)	$ 17.1
Pension Benefits
Components of Net Periodic Benefit Cost [Abstract]
Service cost	2.6	2.6	2.4
Interest cost	8.3	7.6	8.2
Expected return on plan assets	(10.7)	(10.9)	(10.5)
Amortization of net loss	4.0	7.7	7.9
Amortization of prior service cost	(0.8)	(0.8)	(0.8)
Curtailment gain	0	0	0
Recognition of loss on special termination benefit	0	0	0.1
Net periodic benefit cost	3.4	6.2	7.3
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (net of tax) [Abstract]
Net loss (gain)	27.1	(24.7)	7.0
Amortization of unrecognized gain (loss)	(4.0)	(7.7)	(7.9)
Amortization of prior service cost	0.8	0.8	0.8
Total recognized in other comprehensive income	23.9	(31.6)	(0.1)
Total recognized in net periodic benefit cost and other comprehensive income	27.3	(25.4)	7.2
Other Post-retirement Benefits
Components of Net Periodic Benefit Cost [Abstract]
Service cost	0.1	0.1	0.1
Interest cost	0.6	0.4	0.5
Expected return on plan assets	0	0	0
Amortization of net loss	0.3	(0.2)	(0.2)
Amortization of prior service cost	0	0	0
Curtailment gain	0	(0.5)	0
Recognition of loss on special termination benefit	0	0	0
Net periodic benefit cost	1.0	(0.2)	0.4
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (net of tax) [Abstract]
Net loss (gain)	(0.6)	3.0	(0.4)
Amortization of unrecognized gain (loss)	(0.3)	0.2	0.3
Amortization of prior service cost	0	0	0
Total recognized in other comprehensive income	(0.9)	3.2	(0.1)
Total recognized in net periodic benefit cost and other comprehensive income	$ 0.1	$ 3.0	$ 0.3