Employee Benefit Plans - Net Periodic Benefit Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Net Periodic Benefit Cost:
Curtailment gain	$ 0	$ (0.9)	$ 0
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income:
Net actuarial (gain) loss	4.8	(3.6)	5.1
Amortization of prior service cost	0	0.1	0.1
Amortization of actuarial (gain) loss	(0.3)	(0.6)	(0.4)
Total net loss (gain) recognized in other comprehensive income	4.5	(4.1)	4.8
Pension Benefits [Member]
Net Periodic Benefit Cost:
Interest cost	1.8	1.6	1.8
Expected return on plan assets	(2.5)	(2.3)	(2.1)
Amortization of prior service credit	0	0	0
Amortization of net actuarial (gain) loss	0.4	0.6	0.4
Curtailment gain	0	0	0
Net periodic benefit (income) cost	(0.3)	(0.1)	0.1
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income:
Net actuarial (gain) loss	5.2	(2.8)	4.7
Amortization of prior service cost	0	0	0
Amortization of actuarial (gain) loss	(0.4)	(0.6)	(0.4)
Total net loss (gain) recognized in other comprehensive income	4.8	(3.4)	4.3
Total recognized in net periodic benefit cost and other comprehensive income	4.5	(3.5)	4.4
Other Post-retirement Benefits [Member]
Net Periodic Benefit Cost:
Interest cost	0.1	0.2	0.2
Expected return on plan assets	0	0	0
Amortization of prior service credit	0	(0.1)	(0.1)
Amortization of net actuarial (gain) loss	(0.1)	0	0
Curtailment gain	0	(0.9)	0
Net periodic benefit (income) cost	0	(0.8)	0.1
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income:
Net actuarial (gain) loss	(0.4)	(0.8)	0.4
Amortization of prior service cost	0	0.1	0.1
Amortization of actuarial (gain) loss	0.1	0	0
Total net loss (gain) recognized in other comprehensive income	(0.3)	(0.7)	0.5
Total recognized in net periodic benefit cost and other comprehensive income	$ (0.3)	$ (1.5)	$ 0.6