Accumulated Other Comprehensive Loss - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (1)	$ 27
Tax impact		(6)
Total after tax	(1)	21
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses	1	1
Amortization of prior service cost	(1)	(1)
Settlement and curtailment (credit) cost	1	$ (27)
Total after tax	$ (1)