Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Pension benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial (gain) loss	$ (191)	$ 21
Amortization of actuarial (loss) gain	(28)	(36)
Amortization of prior service credit/(cost)	9	9
Total recognized in other comprehensive income	(210)	(6)
Total recognized in net periodic benefit cost and other comprehensive income	(174)	44
Other postretirement benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Current year actuarial (gain) loss	(4)	(3)
Amortization of actuarial (loss) gain	1	0
Amortization of prior service credit/(cost)	3	3
Total recognized in other comprehensive income	0	0
Total recognized in net periodic benefit cost and other comprehensive income	$ (3)	$ (2)