Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Income Tax Disclosure [Abstract]
Effective Income Tax Rate, Continuing Operations	32.00%	20.00%	30.00%	28.00%
Tax benefit recognized related to CA apportionment rules	$ 76,000,000
Income Tax Impact From Remeasurement Of Deferred Taxes		208,000,000		208,000,000
Unrecognized Tax Benefits, Period Increase (Decrease)	338,000,000		221,000,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate, Period Increase (Decrease)	247,000,000		171,000,000
Unrecognized Tax Benefits, Change in Interest on Income Taxes Accrued	3,000,000	7,000,000	5,000,000	14,000,000
Increase (decrease) In Unrecognized Tax Benefits, Penalties On Income Taxes Accrued	1,000,000		2,000,000
Reclassification from deferred tax assets to income tax receivable			1,600,000,000
Payments from litigation escrow account—retrospective responsibility plan			$ 4,383,000,000	$ 140,000,000