Employee Benefit Plans - Components of Net Periodic Defined Benefit Pension Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2.7	$ 2.5	$ 5.6	$ 5.1
Interest cost	4.4	6.4	9.0	12.7
Expected return on plan assets	(5.3)	(6.3)	(10.7)	(12.5)
Amortization if unrecognized prior service cost	0.2	0.2	0.4	0.4
Recognized actuarial losses (gains)	3.8	2.8	7.6	5.6
Total	5.8	5.6	11.9	11.3
OPEB
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.1	0.1
Interest cost		0.1	0.2	0.3
Amortization if unrecognized prior service cost	(0.4)	(0.6)	(0.9)	(1.1)
Recognized actuarial losses (gains)	(0.1)	(0.1)	(0.1)	(0.1)
Total	$ (0.4)	$ (0.5)	$ (0.7)	$ (0.8)