Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Net unrealized actuarial gain			$ 56
Amortization of:
Curtailment gain			(8)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 0	$ 12	13	$ 35
Interest cost	9	10	30	30
Expected return on assets	(17)	(18)	(52)	(54)
Amortization of:
Prior service credit	0	(2)	(1)	(5)
Actuarial loss (gain)	2	0	6	0
Curtailment gain	0	0	(8)	0
Settlement loss	0	1	0	5
Total net periodic benefit cost	(6)	3	(12)	11
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)