Net Periodic Benefit Expenses Recognized for Post-Retirement Plans (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Amortization of net prior service costs from earlier periods
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	18.4	19.8	18.9
Interest cost	16.5	13.5	13.1
Expected return on plan assets	(14.3)	(12.9)	(12.5)
Amortization of net actuarial loss from earlier periods	6.6	10.8	9.1
Amortization of net prior service costs from earlier periods	0.7	0.6	0.7
Net periodic expense	27.9	31.8	29.3
Other Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	1.7	1.7	1.5
Interest cost	0.9	0.8	0.7
Expected return on plan assets
Amortization of net actuarial loss from earlier periods		0.3	0.3
Amortization of net prior service costs from earlier periods
Net periodic expense	$ 2.6	$ 2.8	$ 2.5