Accumulated Other Comprehensive Income (Loss) - (Detail 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income			$ 45
Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	$ 18	$ 17	55	$ 51
Other comprehensive (income) loss, amortization adjustment from AOCI, pension and other postretirement benefit plans, for net prior service cost (credit), benefit	(6)	(6)	(19)	(17)
Amounts reclassified into income	12	11	36	33
Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	5	2	14	7
Other comprehensive income (loss), reclassification adjustment from AOCI on derivatives, tax	(2)	(1)	(5)	(3)
Amounts reclassified into income	$ 3	$ 2	$ 9	$ 4