Benefit Plans - Net Pension and Other Postretirement Cost (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
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 18	$ 21	$ 35	$ 42
Interest cost	23	22	46	43
Expected return on plan assets	(31)	(29)	(62)	(58)
Amortization of prior service credit	(4)	(3)	(8)	(7)
Amortization of loss	12	19	24	38
Net pension and postretirement cost	18	29	35	58
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	3
Interest cost	2	3	5	5
Expected return on plan assets
Amortization of prior service credit	(1)		(2)	(1)
Amortization of loss	1	1	1	2
Net pension and postretirement cost	$ 2	$ 5	$ 6	$ 9