Recently Issued Accounting Standards (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Mar. 31, 2016
Mar. 31, 2015
Sep. 30, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Income Tax Benefit $ (63) $ (78) $ (87) $ (127)  
Excess Tax Benefit from Share-based Compensation, Operating Activities [1]     0 $ (9)  
New Accounting Pronouncement, Early Adoption, Effect [Member]          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Income Tax Benefit     3    
Excess Tax Benefit from Share-based Compensation, Operating Activities     $ 3    
Reclass from Deferred Tax Assets, Net of Valuation Allowance, Current         $ 9
Reclass from Deferred Tax Liabilities, Net, Current         $ 84
[1] The Company adopted ASU 2016-09 (see Note 2) during the three months ended March 31, 2016, which requires excess tax benefits from stock-based compensation to be classified within operating cash flow consistent with other cash flows associated with income taxes. The Company elected to adopt ASU 2016-09 prospectively, therefore prior years have not been adjusted.