Fair Value Measurements and Investments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
Jun. 30, 2014	Sep. 30, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of exercise by Visa Europe	40.00%
P/E differential at the time of exercise	1.9x
P/E differential at the time of exercise, ratio	190.00%
Spot price to earnings	20.3x
Spot price to earnings, ratio	2030.00%
Incremental price to earnings differential compared to estimate	1.5x
Incremental price to earnings differential compared to estimate, ratio	150.00%
Incremental probability of exercise by Visa Europe	5.00%
Increase in put option value due to increase in probability of exercise	$ 18
Incremental assumed price to earnings differential at time of exercise	1.0x
Incremental P/E differential at time of exercise, ratio	100.00%
Increase in put option value due to increase in price to earnings differential	84
Other than temporary impairment loss	15
Available-for-sale securities, gross unrealized gains	91	93
Available-for-sale securities, gross unrealized losses		1
Non Marketable Equity Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-marketable equity investments	32	30
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Visa Europe put option	$ 145	$ 145

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.