Number of Shares of Class A Common Shares Outstanding on an As-Converted Basis (Detail) In Millions, unless otherwise specified	Mar. 31, 2013		Sep. 30, 2012
Schedule of Common Stock as Converted [Line Items]
As-converted Class A Common Stock(1)	651	[1]
Class A common stock
Schedule of Common Stock as Converted [Line Items]
Shares Outstanding	519		535
Conversion Rate Into Class A Common Stock
As-converted Class A Common Stock(1)	519	[1]
Class B common stock
Schedule of Common Stock as Converted [Line Items]
Shares Outstanding	245		245
Conversion Rate Into Class A Common Stock	0.4206
As-converted Class A Common Stock(1)	103	[1]
Class C common stock
Schedule of Common Stock as Converted [Line Items]
Shares Outstanding	29		31
Conversion Rate Into Class A Common Stock	1.0000
As-converted Class A Common Stock(1)	29	[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.