Related Parties Related Parties (Details)	12 Months Ended
	Sep. 30, 2018 USD ($) entity	Sep. 30, 2017 USD ($) entity	Sep. 30, 2016 USD ($)
Related Party Transactions [Abstract]
Minimum ownership of Visa stock to be considered a related party, percent	10.00%
Minimum ownership interest in investee to be considered a related party, percent	10.00%
Number of entities owning more than 10% of Visa's total voting stock | entity	0	0
Significant transactions with related parties | $	$ 0	$ 0	$ 0