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, 2019	Sep. 30, 2018
Deferred Tax Assets:
Accrued compensation and benefits	$ 117	$ 135
Accrued litigation obligation	273	329
Client incentives	125	213
Net operating loss carryforwards	65	34
Comprehensive loss	33	17
Federal benefit of state taxes	148	120
Other	6	127
Valuation allowance	(69)	(34)
Deferred tax assets	698	941
Deferred Tax Liabilities:
Property, equipment and technology, net	(314)	(286)
Intangible assets	(4,983)	(5,153)
Foreign taxes	(184)	(106)
Deferred tax liabilities	(5,481)	(5,545)
Net deferred tax liabilities	$ (4,783)	$ (4,604)