Accumulated Other Comprehensive (Loss) Income - Accumulated Other Comprehensive (Loss) Income (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	$ 13
Benefit Plans Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	11	9
Unrealized Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	$ 1	$ 1