Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 43	$ 38	$ 41
Interest cost	35	40	38
Expected return on assets	(61)	(55)	(54)
Prior service credit	(9)	(9)	(9)
Actuarial loss (gain)	28	33	19
Net benefit cost	36	47	35
Settlement loss	0	3	2
Total net periodic benefit cost	36	50	37
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0
Interest cost	1	1	1
Expected return on assets	0	0	0
Prior service credit	(3)	(3)	(3)
Actuarial loss (gain)	(1)	0	(1)
Net benefit cost	(3)	(2)	(3)
Settlement loss	0	0
Total net periodic benefit cost	$ (3)	$ (2)	$ (3)