Collateral (Detail) - USD ($) $ in Millions		Jun. 30, 2018	Sep. 30, 2017
Settlement Guarantee Management [Abstract]
Cash equivalents	[1]	$ 1,746	$ 1,490
Pledged securities at market value		164	167
Letters of credit		1,349	1,316
Guarantees		677	941
Total		$ 3,936	$ 3,914

[1] Cash collateral held by Visa Europe is not included on the Company’s consolidated balance sheets as its clients retain beneficial ownership and the cash is only accessible to the Company in the event of default by the client on its settlement obligations.