Employee Benefit Plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.9	$ 2.6
Interest cost	4.6	6.3
Expected return on plan assets	(5.4)	(6.2)
Amortization of unrecognized prior service cost	0.2	0.2
Recognized actuarial losses (gain)	3.8	2.8
Total	6.1	5.7
OPEB
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0.2	0.2
Amortization of unrecognized prior service cost	(0.5)	(0.5)
Total	$ (0.3)	$ (0.3)