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Number of Shares of Class A Common Shares Outstanding on an As-Converted Basis (Detail)
In Millions, unless otherwise specified
12 Months Ended
Sep. 30, 2013
conversion_rate
Sep. 30, 2012
Class of Stock [Line Items]    
As-converted Class A Common Stock 638 [1]  
Class A common stock
   
Class of Stock [Line Items]    
Common stock, shares, outstanding 508 535
Conversion Rate Into Class A Common Stock 0  
As-converted Class A Common Stock 508 [1]  
Class B common stock
   
Class of Stock [Line Items]    
Common stock, shares, outstanding 245 245
Conversion Rate Into Class A Common Stock 0.4206  
As-converted Class A Common Stock 103 [1]  
Class C common stock
   
Class of Stock [Line Items]    
Common stock, shares, outstanding 27 31
Conversion Rate Into Class A Common Stock 1.0000  
As-converted Class A Common Stock 27 [1]  
[1] Figures in the table may not recalculate exactly due to rounding. As-converted class A common stock is calculated based on whole numbers, not the rounded numbers presented.