Retrospective Responsibility Plan Changes in the Escrow Account (Details) (USD $) In Millions, unless otherwise specified			6 Months Ended
	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2013 Class plaintiffs		Mar. 31, 2013 Individual plaintiffs
Escrow Account [Roll Forward]
Balance at October 1, 2012	$ 49	$ 4,432
Payments to settlement funds(1):			(4,033)	[1]	(350)	[1]
Balance at March 31, 2013	$ 49	$ 4,432

[1] These payments are associated with the Multidistrict Litigation Proceedings. The settlement with the class plaintiffs in these proceedings is subject to final court approval, which the Company cannot assure will be received, and to the adjudication of any appeals. See Note 11—Legal Matters.