Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Sep. 30, 2013
Accrued liabilities
Visa Europe put option	$ 145	$ 145
Level 1
Prepaid and other current assets:
Fair value, total assets	3,528	2,920
Accrued liabilities
Fair value, total liabilities	0	0
Level 2
Prepaid and other current assets:
Fair value, total assets	3,027	3,047
Accrued liabilities
Fair value, total liabilities	20	15
Level 3
Prepaid and other current assets:
Fair value, total assets	7	7
Accrued liabilities
Fair value, total liabilities	145	145
Visa Europe put option | Level 3
Accrued liabilities
Visa Europe put option	145	145
Foreign exchange derivative instruments | Level 2
Accrued liabilities
Foreign exchange derivative instruments	20	15
Money market funds | Level 1
Cash equivalents and restricted cash:
Cash equivalents and restricted cash:	1,763	1,071
Commercial paper | Level 2
Cash equivalents and restricted cash:
Cash equivalents and restricted cash:	43	51
Equity securities | Level 1
Investment securities:
Trading securities	82	75
Available-for-sale securities	131	101
U.S. government-sponsored debt securities | Level 2
Investment securities:
Available-for-sale securities	2,480	2,704
U.S. Treasury securities | Level 1
Investment securities:
Available-for-sale securities	1,552	1,673
Corporate Debt Securities | Level 2
Investment securities:
Available-for-sale securities	488	269
Auction rate securities | Level 3
Investment securities:
Available-for-sale securities	7	7
Foreign exchange derivative instruments | Level 2
Prepaid and other current assets:
Prepaid and other current assets:	$ 16	$ 23