Accumulated Other Comprehensive (Loss) Income - Accumulated Other Comprehensive (Loss) Income (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income			$ 38
Benefit Plans Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	$ 11	$ 8	33	$ 25
Unrealized Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	$ 2	$ 1	$ 4	$ 4