Investments - Schedule of Allowance for Credit Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Document Period End Date	Dec. 31, 2013
Allowance for credit losses:
Balance at beginning of period	$ 5.2	$ 1.4
Provision for credit losses	1.8	1.2
Balance at end of period	$ 7.0	$ 2.6