v3.3.0.814
Stockholders' Equity Share Repurchases in the Open Market (Details) - USD ($)
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2013
Class of Stock [Line Items]      
Total cost $ 2,910 $ 4,118 $ 5,365
Class A common stock      
Class of Stock [Line Items]      
Shares repurchased in the open market [1] 44 79  
Average repurchase price per share [2] $ 65.98 $ 52.12  
Total cost $ 2,910 $ 4,118  
[1] All shares repurchased in the open market have been retired and constitute authorized but unissued shares.
[2] Figures in the table may not recalculate exactly due to rounding. Average repurchase price per share is calculated based on unrounded numbers.