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Commitments and Contingencies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012
Commitments and Contingencies Disclosure [Abstract]
Reserves for environmental liabilities	$ 28	$ 25	$ 26
Conditional asset retirement obligations	$ 81	$ 76	$ 84

Total costs accrued as of the balance sheet date for environmental loss contingencies.

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- Definition

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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