Retrospective Responsibility Plan Changes in the Escrow Account (Details) (USD $)
6 Months Ended
Mar. 31, 2015
Sep. 30, 2014
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted Cash and Cash Equivalents $ 1,200,000,000 $ 1,500,000,000
Opt-out Merchants [Member]    
Restricted Cash and Cash Equivalents Items [Line Items]    
Payments to opt-out merchants $ 321,000,000