Components of Net Periodic Benefit Cost (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 11	$ 10
Interest cost	10	9
Expected return on assets	(17)	(16)
Amortization of:
Prior service credit	(2)	(2)
Actuarial loss		7
Settlement loss	1
Total net periodic benefit cost	3	8
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost
Interest cost
Expected return on assets
Amortization of:
Prior service credit	(1)	(1)
Actuarial loss
Settlement loss	0	0
Total net periodic benefit cost	$ (1)	$ (1)