Other Required Disclosures - Schedule of Other Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Feb. 14, 2013	Sep. 30, 2012
Other liabilities:
Amounts payable for investment purchases	$ 30.9		$ 206.7
Retained asset account	202.9		203.7
Amounts payable to reinsurers	47.7		32.0
Remittances and items not allocated	37.3		29.5
Oil and natural gas asset-retirement obligations	24.8	18.5	0
Other	96.0		128.7
Total other liabilities	$ 439.6		$ 600.6