Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) (USD $) In Millions, unless otherwise specified					6 Months Ended
	Mar. 31, 2013	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2011	Mar. 31, 2013 Settled	Mar. 31, 2012 Settled	Mar. 31, 2013 Unsettled		Mar. 31, 2012 Unsettled
Loss Contingency Accrual [Roll Forward]
Balance at October 1	$ 6	$ 4,386	$ 286	$ 425
Provision for unsettled matters							4
Interest accretion on settled matters						1
Payments to settlement funds					(351)	(140)	(4,033)	[1]		[1]
Balance at March 31	$ 6	$ 4,386	$ 286	$ 425

[1] On December 10, 2012, the Company paid approximately $4.0 billion from the litigation escrow account into a settlement fund established pursuant to the definitive class settlement agreement in the Multidistrict Litigation Proceedings. The settlement with the class plaintiffs is subject to final court approval, which the Company cannot assure will be received, and to the adjudication of any appeals. See further discussion below.