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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2016	Sep. 30, 2015	Mar. 31, 2015
Investment securities:
Trading	$ 69	$ 66
Accrued liabilities
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	0		$ 0
Level 1 \| Fair Value, Measurements, Recurring
Prepaid and other current assets:
Fair value, total assets	15,079	5,777
Accrued liabilities
Fair value, total liabilities	0	0
Level 2 \| Fair Value, Measurements, Recurring
Prepaid and other current assets:
Fair value, total assets	7,832	3,504
Accrued liabilities
Fair value, total liabilities	114	13
Level 3 \| Fair Value, Measurements, Recurring
Prepaid and other current assets:
Fair value, total assets	0	7
Accrued liabilities
Fair value, total liabilities	0	255
Visa Europe put option \| Level 3 \| Fair Value, Measurements, Recurring
Accrued liabilities
Visa Europe put option	0	255
Foreign exchange derivative instruments \| Level 2 \| Fair Value, Measurements, Recurring
Accrued liabilities
Foreign exchange derivative instruments	114	13
Money market funds \| Level 1 \| Fair Value, Measurements, Recurring
Cash equivalents and restricted cash:
Cash equivalents and restricted cash:	6,765	3,051
U.S. Treasury securities \| Level 1 \| Fair Value, Measurements, Recurring
Cash equivalents and restricted cash:
Cash equivalents and restricted cash:	5,099	0
Investment securities:
Available-for-sale securities	3,079	2,656
U.S. government-sponsored debt securities \| Level 2 \| Fair Value, Measurements, Recurring
Cash equivalents and restricted cash:
Cash equivalents and restricted cash:	3,328	280
Investment securities:
Available-for-sale securities	4,043	2,615
Equity securities \| Level 1 \| Fair Value, Measurements, Recurring
Investment securities:
Trading	69	66
Available-for-sale securities	67	4
Corporate debt securities \| Level 2 \| Fair Value, Measurements, Recurring
Investment securities:
Available-for-sale securities	273	533
Auction rate securities \| Level 3 \| Fair Value, Measurements, Recurring
Investment securities:
Available-for-sale securities	0	7
Foreign exchange derivative instruments \| Level 2 \| Fair Value, Measurements, Recurring
Prepaid and other current assets:
Prepaid and other current assets:	$ 188	$ 76