Pension and Post-Retirement Benefits - Components of Net Periodic Benefit Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Net periodic benefit (income) costs:
Defined Benefit Plan, Net Periodic Benefit Cost	$ (1.4)	$ (0.1)	$ (4.0)	$ (0.3)	$ (0.4)
Pension Plans
Net periodic benefit (income) costs:
Service cost	0.2	0.3	0.6	0.7
Interest cost	7.5	6.9	22.6	20.7
Expected return on plan assets	(10.3)	(9.6)	(31.0)	(28.7)
Amortization of actuarial loss	1.1	2.1	3.3	6.4
Defined Benefit Plan Net Periodic Benefit Cost Before Portion Allocated To Affiliate	(1.5)	(0.3)	(4.5)	(0.9)
Defined Benefit Plan Net Periodic Benefit Cost Portion Allocated To Affiliate	(0.1)	0	(0.1)	(0.1)
Defined Benefit Plan, Net Periodic Benefit Cost	(1.6)	(0.3)	(4.6)	(1.0)
Other Post-Retirement Benefit Plans
Net periodic benefit (income) costs:
Service cost	0	0	0	0
Interest cost	0.2	0.1	0.5	0.4
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	0	0.1	0.1	0.3
Defined Benefit Plan Net Periodic Benefit Cost Before Portion Allocated To Affiliate	0.2	0.2	0.6	0.7
Defined Benefit Plan Net Periodic Benefit Cost Portion Allocated To Affiliate	0	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	$ 0.2	$ 0.2	$ 0.6	$ 0.7