Commitments and Contingencies - Additional Information (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Sep. 30, 2015 |
Sep. 30, 2014 |
Sep. 30, 2013 |
|
| Other Commitments [Line Items] | |||
| Rent expense incurred | $ 136 | $ 134 | $ 94 |
| Minimum | |||
| Other Commitments [Line Items] | |||
| Client Incentive Agreement Period | 1 year | ||
| Maximum | |||
| Other Commitments [Line Items] | |||
| Client Incentive Agreement Period | 13 years | ||