Defined Benefit Plans - Obligations and Funded Status (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended	12 Months Ended			3 Months Ended
	Dec. 31, 2012	Jun. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Mar. 31, 2014
Change in the Projected Benefit Obligation (PBO):
Plan amendments	$ 29.8	$ 34.7
Actuarial loss (gain)			13.7	5.2	42.2
Change in Plan Assets:
Fair value of plan assets at beginning of year			583.8			583.8
Fair value of plan assets at end of year			608.2	583.8
Pension Benefits
Change in the Projected Benefit Obligation (PBO):
Projected benefit obligation at beginning of year		722.5	662.3	722.5		662.3
Service cost			10.4	11.4
Interest cost			32.9	30.1
Actuarial loss (gain)			133.1	(73.0)
Benefits paid			(30.1)	(28.7)
Projected benefit obligation at end of year			808.6	662.3
Accumulated benefit obligation at end of year (excludes the impact of future compensation increases)			793.2	648.5
Change in Plan Assets:
Fair value of plan assets at beginning of year		536.8	583.8	536.8		583.8
Actual return on plan assets			52.0	74.6
Employer contributions			2.5	1.1
Benefits paid			(30.1)	(28.7)
Fair value of plan assets at end of year			608.2	583.8
Funded status (Fair value of plan assets less PBO)			(200.4)	(78.5)
Postretirement Benefits
Change in the Projected Benefit Obligation (PBO):
Projected benefit obligation at beginning of year		73.3	34.2	73.3		34.2
Service cost			0.1	0.3
Interest cost			0.8	1.7
Plan amendments			(15.3)	(34.7)		15.3
Actuarial loss (gain)		4.0	3.9	(0.3)		0.6
Participants' contributions			0.3	0.5
Benefits paid			(4.2)	(7.0)
Medicare Part D reimbursement			0.4	0.4
Foreign exchange			(0.1)
Projected benefit obligation at end of year			20.1	34.2
Change in Plan Assets:
Employer contributions			3.5	6.1
Participants' contributions			0.3	0.5
Medicare Part D reimbursement			0.4	0.4
Benefits paid			(4.2)	(7.0)
Funded status (Fair value of plan assets less PBO)			$ (20.1)	$ (34.2)