Legal Matters (Tables)
 6 Months Ended
Mar. 31, 2015
Loss Contingencies [Line Items]  
Schedule of Loss Contingencies by Contingency
The following table summarizes activity related to accrued litigation.
 
Fiscal 2015
 
Fiscal 2014
 
(in millions)
Balance at October 1
$
1,456

 
$
5

Reestablishment of obligation related to interchange multidistrict litigation
—

 
1,056

  Additional provision for legal matters
3

 
—

Payments on legal matters
(324
)
 
(1
)
Balance at March 31
$
1,135

 
$
1,060
Covered Litigation [Member]  
Loss Contingencies [Line Items]  
Schedule of Loss Contingencies by Contingency
The following table summarizes the activity related to covered litigation.
 
Fiscal 2015
 
Fiscal 2014
 
(in millions)
Balance at October 1
$
1,449

 
$
—

Payments on covered litigation
(321
)
 
—

Reestablishment of obligation related to interchange multidistrict litigation
—

 
1,056

Balance at March 31
$
1,128

 
$
1,056