Fair Value Measurements and Investments (Tables)
 6 Months Ended
Mar. 31, 2015
Fair Value Disclosures [Abstract]  
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis
Assets and Liabilities Measured at Fair Value on a Recurring Basis
 
Fair Value Measurements
Using Inputs Considered as
 
Level 1
 
Level 2
 
Level 3
 
March 31,
2015
 
September 30,
2014
 
March 31,
2015
 
September 30,
2014
 
March 31,
2015
 
September 30,
2014
 
(in millions)
Assets
 
 
 
 
 
 
 
 
 
 
 
Cash equivalents and restricted cash:
 
 
 
 
 
 
 
 
 
 
 
Money market funds
$
2,160

 
$
2,277

 
 
 
 
 
 
 
 
Commercial paper
 
 
 
 
$
48

 
$
37

 
 
 
 
Investment securities, trading:
 
 
 
 
 
 
 
 
 
 
 
Equity securities
71

 
69

 
 
 
 
 
 
 
 
Investment securities, available-for-sale:
 
 
 
 
 
 
 
 
 
 
 
U.S. government-sponsored debt securities
 
 
 
 
2,112

 
2,162

 
 
 
 
U.S. Treasury securities
2,580

 
2,176

 
 
 
 
 
 
 
 
Equity securities
13

 
58

 
 
 
 
 
 
 
 
Corporate debt securities
 
 
 
 
563

 
522

 
 
 
 
Auction rate securities
 
 
 
 
 
 
 
 
$
7

 
$
7

Prepaid and other current assets:
 
 
 
 
 
 
 
 
 
 
 
Foreign exchange derivative instruments
 
 
 
 
119

 
40

 
 
 
 
Total
$
4,824

 
$
4,580

 
$
2,842

 
$
2,761

 
$
7

 
$
7

Liabilities
 
 
 
 
 
 
 
 
 
 
 
Accrued liabilities:
 
 
 
 
 
 
 
 
 
 
 
Visa Europe put option
 
 
 
 
 
 
 
 
$
145

 
$
145

Foreign exchange derivative instruments
 
 
 
 
$
11

 
$
6

 
 
 
 
Total
$
—

 
$
—

 
$
11

 
$
6

 
$
145

 
$
145