Other Required Disclosures - Schedule of Other Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Feb. 14, 2013	Sep. 30, 2012
Other liabilities:
Amounts payable for investment purchases	$ 95.7		$ 206.7
Retained asset account	208.2		203.7
Amounts payable to reinsurers	30.1		32.0
Remittances and items not allocated	36.4		29.5
Oil and natural gas asset-retirement obligations	24.3	18.5	0
Other	94.2		128.7
Total other liabilities	$ 488.9		$ 600.6

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Aggregate amounts payable to broker-dealers and clearing organizations include amounts payable for securities failed to receive, certain deposits received for securities loaned, amounts payable to clearing organizations on open transactions, and floor-brokerage payables. In addition, the net receivable or payable arising from unsettled trades would be reflected in those captions. A broker-dealer that purchases securities, either for its own account or for a customer's account, but does not receive the securities on the settlement date records the amount of money representing the purchase price of the securities, including any accrued interest, as a liability to the selling broker-dealer. This liability is paid when the securities are received by the purchasing broker-dealer.

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