Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 41	$ 45	$ 51
Interest cost	38	40	46
Expected return on assets	(54)	(50)	(45)
Prior service credit	(9)	(9)	(8)
Actuarial loss (gain)	19	16	14
Net benefit cost	35	42	58
Settlement loss	2		3
Total net periodic benefit cost	37	42	61
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	2
Prior service credit	(3)	(3)	(3)
Actuarial loss (gain)	(1)	(1)
Net benefit cost	(3)	(3)	(1)
Total net periodic benefit cost	$ (3)	$ (3)	$ (1)