Pensions and Postretirement Benefits (Summary of Change in Defined Benefit and Postretirement Benefit Plans) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Apr. 30, 2011	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in benefit obligation
Plan amendment	$ 1.1
Change in plan assets
Fair value of plan assets at end of year		125.7	125.4
Funded (underfunded) status of the plans
Current liabilities		1.6	1.7
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year		52.1	56.4
Service costs		2.2	2.6	2.2
Interest costs		2.2	2.0	2.2
Actuarial (gains) losses		8.8	(4.4)
Plan amendment		0.4	0
Benefits and expenses paid, net of contributions		(4.6)	(4.5)
Benefit obligation at end of year		61.1	52.1	56.4
Change in plan assets
Fair value of plan assets at beginning of year		125.4	109.4
Actual return on plan assets		5.8	21.8
Company contributions		0	0
Cash transfer to fund postretirement benefit payments		(0.9)	(1.3)
Benefits and expenses paid, net of contributions		(4.6)	(4.5)
Fair value of plan assets at end of year		125.7	125.4	109.4
Funded (underfunded) status of the plans		64.6	73.3
Funded (underfunded) status of the plans
Noncurrent assets		64.6	73.3
Noncurrent liabilities		0	0
Current liabilities		0	0
Total assets (liabilities) recognized in the consolidated balance sheets		64.6	73.3
Amounts recognized in accumulated other comprehensive loss
Net actuarial loss		15.3	2.1
Net prior service cost (credit)		0.4	0.1
Accumulated other comprehensive loss		15.7	2.2
Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year		16.2	18.5
Service costs		0	0.1	0
Interest costs		0.6	0.6	0.8
Actuarial (gains) losses		1.9	(1.3)
Plan amendment		0	0
Benefits and expenses paid, net of contributions		(1.7)	(1.7)
Benefit obligation at end of year		17.0	16.2	18.5
Change in plan assets
Fair value of plan assets at beginning of year		0	0
Actual return on plan assets		0	0
Company contributions		1.7	1.7
Cash transfer to fund postretirement benefit payments		0	0
Benefits and expenses paid, net of contributions		(1.7)	(1.7)
Fair value of plan assets at end of year		0	0	0
Funded (underfunded) status of the plans		(17.0)	(16.2)
Funded (underfunded) status of the plans
Noncurrent assets		0	0
Noncurrent liabilities		15.4	14.5
Current liabilities		1.6	1.7
Total assets (liabilities) recognized in the consolidated balance sheets		(17.0)	(16.2)
Amounts recognized in accumulated other comprehensive loss
Net actuarial loss		7.6	6.3
Net prior service cost (credit)		(0.4)	(0.5)
Accumulated other comprehensive loss		$ 7.2	$ 5.8