Accumulated Other Comprehensive Loss - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (1)				$ (2)	$ 28
Tax impact					1	(6)
Total after tax	(1)	$ 1	$ (1)		(1)	22
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses				$ 1	2	3
Amortization of prior service credit	(1)			$ (1)	(3)	(2)
Settlement and curtailment (credit) cost					$ (1)	$ 27
Total after tax	$ (1)	$ 1	$ (1)