Restructuring - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Restructuring Cost And Reserve [Line Items]
Restructuring costs		$ 2,000,000
Cash payments	$ 2,000,000	13,000,000
Employee-Related Costs
Restructuring Cost And Reserve [Line Items]
Cash payments	2,000,000	10,000,000
Real Estate Costs
Restructuring Cost And Reserve [Line Items]
Restructuring costs		2,000,000
Cash payments		3,000,000
Restructuring Plan
Restructuring Cost And Reserve [Line Items]
Restructuring costs related to close of acquisition	0	74,000,000
Restructuring costs		2,000,000	$ 50,000,000
Cash payments	$ 74,000,000
Restructuring Plan | Employee-Related Costs
Restructuring Cost And Reserve [Line Items]
Restructuring costs related to close of acquisition		67,000,000
Restructuring costs			45,000,000
Restructuring Plan | Real Estate Costs
Restructuring Cost And Reserve [Line Items]
Restructuring costs related to close of acquisition		6,000,000
Restructuring costs		2,000,000	4,000,000
Restructuring Plan | Other Costs
Restructuring Cost And Reserve [Line Items]
Restructuring costs related to close of acquisition		$ 1,000,000
Restructuring costs			$ 1,000,000