Fair Value Measurements and Investments - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2015	Sep. 30, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Visa Europe Purchase Price	$ 15,000
Probability of exercise by Visa Europe	40.00%	40.00%
P/E differential at the time of exercise, ratio	140.00%	190.00%
Spot price to earnings, ratio	2250.00%
Incremental price to earnings differential compared to estimate, ratio	160.00%
Incremental probability of exercise by Visa Europe	5.00%
Increase in put option value due to increase in probability of exercise	$ 32
Incremental P/E differential at time of exercise, ratio	100.00%
Increase in put option value due to increase in price to earnings differential	$ 259
Non-marketable equity investments	43	$ 35
Goodwill and Intangible Asset Impairment	0
Available-for-sale securities, gross unrealized gains	9	48
Available-for-sale securities, gross unrealized losses	3	0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Visa Europe put option	$ 255	$ 145
Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities, stated maturities	1 year
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investment securities, stated maturities	2 years