Business Restructuring Charges Business Restructuring Charges - Changes in Restructuring Balance (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Restructuring Reserve [Roll Forward]
Beginning balance	$ 69	$ 62	$ 0
Assumed liability			19
Charged to expense	85	526	271
Cash payments	(57)	(148)	(94)
Non-cash settlements	(9)	(39)	(44)
Other adjustments	(33)	(332)	(91)
Ending balance	55	69	62
Employee Termination
Restructuring Reserve [Roll Forward]
Beginning balance	67	62	0
Assumed liability			19
Charged to expense	27	81	126
Cash payments	(45)	(76)	(74)
Non-cash settlements	0	0	0
Other adjustments	0	0	(9)
Ending balance	49	67	62
Other
Restructuring Reserve [Roll Forward]
Beginning balance	2	0	0
Assumed liability			0
Charged to expense	58	445	146
Cash payments	(12)	(72)	(20)
Non-cash settlements	(9)	(39)	(44)
Other adjustments	(33)	(332)	(81)
Ending balance	$ 6	$ 2	$ 0