Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Amortization of Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ 1		$ 4	$ 2
Amortization of Prior Service Credit [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (1)	$ (1)	(2)	(3)
Settlement and Curtailment (Credit) Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax				(1)
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		(1)	2	(2)
Tax impact				1
Total after tax		$ (1)	$ 2	$ (1)