Shareholders' Equity - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 60	$ 50	$ 38
Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	73	67	51
Other Comprehensive (Income) Loss, Amortization Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Prior Service Cost (Credit), Tax	(25)	(23)	(17)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	48	44	33
Cash Flow Hedges
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	19	10	8
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	(7)	(4)	(3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	$ 12	$ 6	$ 5