Expected Reduction of Revenue for Volume and Support Incentive Agreements (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2017 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Client incentives, 2018	$ 5,049
Client incentives, 2019	4,654
Client incentives, 2020	4,117
Client incentives, 2021	3,658
Client incentives, 2022	3,102
Client incentives, Thereafter	5,080
Client incentives	$ 25,660