Components of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Net Actuarial Gain (Loss), before Tax	$ 56
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	13	$ 12
Interest cost	11	10
Expected return on assets	(17)	(18)
Amortization of:
Prior service credit	(1)	(2)
Actuarial loss	2	0
Curtailment gain	(8)	0
Settlement loss	0	2
Total net periodic benefit cost	0	4
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0
Interest cost	0	0
Expected return on assets	0	0
Amortization of:
Prior service credit	(1)	(1)
Actuarial loss	0	0
Curtailment gain	0	0
Settlement loss	0	0
Total net periodic benefit cost	$ (1)	$ (1)