Stockholders' Equity - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended			6 Months Ended			0 Months Ended		6 Months Ended	0 Months Ended		3 Months Ended	6 Months Ended	42 Months Ended
	Feb. 08, 2012	Dec. 31, 2011		Mar. 31, 2012	Mar. 31, 2012 Deposit into Litigation Escrow	Mar. 31, 2012 Open Market	Dec. 31, 2011 Class A common stock		Mar. 31, 2012 Class A common stock	Dec. 31, 2011 Class C common stock		Mar. 31, 2012 Class C common stock	Mar. 31, 2012 Class C common stock	Mar. 31, 2012 Class C common stock
Stockholders Equity Note [Line Items]
Payments to reduce as converted common stock									$ 1,600,000,000
As converted Class A common stock shares reducted									16.2
Class A common stock repurchased, value				75,000,000		75,000,000
Deposit into the litigation escrow account				1,565,000,000	1,565,000,000
Authorized funds under share repurchase plan	500,000,000
Shares of class C common stock released from transfer restrictions														152
Converted shares		673	[1]				528	[1]		41	[1]	3	6	110
Dividends, date declared				Apr. 26, 2012
Dividends, per share amount declared (in dollars per share)				$ 0.22
Dividends, paid date				Jun. 05, 2012
Dividends, record date				May 18, 2012
Dividends, paid				$ 300,000,000

[1] Figures may not sum due to rounding. As-converted class A common stock count calculated based on whole numbers.