Accumulated Other Comprehensive Income - Schedule of Accumulated Other Comprehensive Income (Loss) (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income			$ 19
Benefit Plans Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	8	14	17	27
Unrealized Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amounts reclassified into income	$ 1	$ 2	$ 2	$ 3