Cash Flows - Actual Employer Contributions (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual employer contributions	$ 0	$ 84
Expected employer contributions
Expected employer contributions	8
Expected benefit payments
Expected benefit payments 2014	116
Expected benefit payments 2015	105
Expected benefit payments 2016	108
Expected benefit payments 2017	100
Expected benefit payments 2018	96
Expected benefit payments 2019-2023	413
Other Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual employer contributions	4	4
Expected employer contributions
Expected employer contributions	4
Expected benefit payments
Expected benefit payments 2014	4
Expected benefit payments 2015	4
Expected benefit payments 2016	3
Expected benefit payments 2017	3
Expected benefit payments 2018	3
Expected benefit payments 2019-2023	$ 10