Investments - Portfolio of Asset-Backed Loans and Other Invested Assets (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Asset-backed loans, by major industry:
Total asset-based loans	$ 565.6	$ 181.5
Less: Allowance for credit losses	5.2	1.4
Total asset-based loans, net	560.4	180.1
Wholesale
Asset-backed loans, by major industry:
Total asset-based loans	56.8	77.2
Apparel
Asset-backed loans, by major industry:
Total asset-based loans	252.9	70.1
Jewelry
Asset-backed loans, by major industry:
Total asset-based loans	125.8	27.9
Other
Asset-backed loans, by major industry:
Total asset-based loans	$ 130.1	$ 6.3