Benefit Plans - Changes in Fair Value of U.S. and Foreign Pension Assets Measured Using Level 3 Inputs (Detail) - U.S. Plans - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Actual return on plan assets:
Beginning fair value	$ 1,255
Ending fair value	1,157	$ 1,255
Other
Actual return on plan assets:
Beginning fair value	193
Ending fair value	123	193
Significant Unobservable Inputs (Level 3)
Actual return on plan assets:
Beginning fair value	4
Ending fair value	2	4
Significant Unobservable Inputs (Level 3) | Other
Actual return on plan assets:
Beginning fair value	4	12
Return on assets	0	1
Purchases, sales and settlements, net	1	4
Transfers (out) in from other categories	(3)	(13)
Exchange rate changes	0	0
Ending fair value	$ 2	$ 4