Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Income Tax Disclosure [Abstract]
Effective income tax rate reconciliation, percent	22.00%		32.00%	27.00%	30.00%
Tax benefit related to a deduction for U.S. domestic production activities				$ 218
Tax benefit related to a deduction for U.S. domestic production activities, from prior periods		17		184
Tax benefit recognized related to CA apportionment rules			(76)
Unrecognized tax benefits, period increase (decrease)	133			180
Unrecognized tax benefits that would impact effective tax rate, period increase (decrease)	132			177
Unrecognized tax benefits, increase resulting from interest accrued	2			4
Unrecognized tax benefits, penalties on income taxes released	$ 1