Investment Income, Net (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Fair Value Measurements and Investments [Abstract]
Interest and dividend income on cash and investments	$ 27	$ 17	$ 16
Gain on other investments	5	17	92
Investment securities, trading:
Unrealized gains (losses) , net	4	9	(5)
Realized gains (losses), net	2	(1)	1
Investment securities, available-for-sale:
Realized gains (losses), net	(1)		4
Other-than-temporary impairment on investments	(15)	(6)
Investment income	$ 22	$ 36	$ 108