Pension and Post-Retirement Benefits - Components of Net Periodic Benefit Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Expected Net Periodic Benefit Cost In Current Fiscal Year	$ (2.4)
Defined Benefit Plan, Net Periodic Benefit Cost	(0.6)	(1.3)	(5.4)
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	0.2	0.2
Defined Benefit Plan, Interest Cost	7.2	7.5
Defined Benefit Plan, Expected Return on Plan Assets	10.1	10.4
Defined Benefit Plan, Amortization of Gains (Losses)	(2.0)	(1.2)
Defined Benefit Plan Net Periodic Benefit Cost Before Portion Allocated To Affiliate	(0.7)	(1.5)
Defined Benefit Plan Net Periodic Benefit Cost Portion Allocated To Affiliate	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	(0.7)	(1.5)
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Service Cost	0	0
Defined Benefit Plan, Interest Cost	0.1	0.2
Defined Benefit Plan, Expected Return on Plan Assets	0	0
Defined Benefit Plan, Amortization of Gains (Losses)	0	0
Defined Benefit Plan Net Periodic Benefit Cost Before Portion Allocated To Affiliate	0.1	0.2
Defined Benefit Plan Net Periodic Benefit Cost Portion Allocated To Affiliate	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	$ 0.1	$ 0.2