Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 12	$ 11	$ 35	$ 34
Interest cost	10	10	30	31
Expected return on assets	(18)	(17)	(54)	(51)
Amortization of:
Prior service credit	(2)	(2)	(5)	(6)
Actuarial loss (gain)	0	1	0	1
Curtailment gain	0	0	0	(3)
Settlement loss	1	2	5	3
Total net periodic benefit cost	3	5	11	9
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	0	0	0	0
Expected return on assets	0	0	0	0
Amortization of:
Prior service credit	0	0	(2)	(2)
Actuarial loss (gain)	(1)	(1)	(1)	(1)
Curtailment gain	0	0	0	0
Settlement loss	0	0	0	0
Total net periodic benefit cost	$ (1)	$ (1)	$ (3)	$ (3)