Income Taxes - Tax Effect of Temporary Differences that Give Rise to Significant Portions of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Deferred Tax Assets:
Accrued compensation and benefits	$ 114	$ 117
Accrued litigation obligation	204	273
Client incentives	121	125
Net operating loss carryforwards	80	65
Comprehensive loss	148	33
Federal benefit of state taxes	203	148
Other	12	6
Valuation allowance	(84)	(69)
Deferred tax assets	798	698
Deferred Tax Liabilities:
Property, equipment and technology, net	(343)	(314)
Intangible assets	(5,492)	(4,983)
Foreign taxes	(137)	(184)
Deferred tax liabilities	(5,972)	(5,481)
Net deferred tax liabilities	$ (5,174)	$ (4,783)