Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified 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]
Total after tax		$ 24
Amortization of Actuarial Losses (Gains) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ 3	(1)	$ 3
Amortization of Prior Service (Credit) Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (3)	4	$ (3)
Settlement Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		27
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		30
Tax impact		(6)
Total after tax		$ 24