Defined Benefit Plans - Components of Consolidated Net Periodic Benefit and Deferred Compensation Benefit Costs and Contributions Made (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Document Period End Date			Mar. 31, 2014
Net periodic benefit cost [Member]
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 0.8	$ 0.9	$ 2.0	$ 1.7
Interest cost	2.6	2.7	6.0	5.3
Expected return on assets	(2.4)	(2.4)	(6.0)	(4.9)
Recognized net actuarial loss	0.4	0.6	0.8	1.1
Defined Benefit Plan, Contributions by Plan Participants	0	(0.1)	0	(0.1)
Net periodic benefit expense	1.4	1.7	2.8	3.1
Contributions made during period	$ 2.2	$ 1.2	$ 5.6	$ 1.9