Accumulated Other Comprehensive Income (Loss) - (Detail 2) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, net of taxes	$ (116)
Income tax benefits recorded for losses recognized in other comprehensive income relating to cash flow hedges		$ 5
Amounts reclassified into income	15
Other comprehensive (income) loss, amortization adjustment from AOCI, pension and other postretirement benefit plans, for net prior service cost (credit), benefit	6	6
Benefit Plans Adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, net of taxes	0
Amounts reclassified into income	12	11
Unrealized Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income before reclassifications, net of taxes	0	(8)
Amounts reclassified into income	$ 3	$ 1