Business Restructuring Charges - Summary of Restructuring Accrual Activity (Detail) $ in Millions	6 Months Ended
	Mar. 31, 2017 USD ($)
Restructuring Reserve [Roll Forward]
Balance at September 30, 2016	$ 69
Charged to expense	46
Cash payments	(45)
Non-cash settlements	(6)
Other adjustments	7
Balance at March 31, 2017	58
Employee Termination
Restructuring Reserve [Roll Forward]
Balance at September 30, 2016	67
Charged to expense	18
Cash payments	(28)
Non-cash settlements	0
Other adjustments	0
Balance at March 31, 2017	57
Other
Restructuring Reserve [Roll Forward]
Balance at September 30, 2016	2
Charged to expense	29
Cash payments	(17)
Non-cash settlements	(6)
Other adjustments	7
Balance at March 31, 2017	$ 1