Stockholders' Equity - Additional Information (Detail) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	1 Months Ended	12 Months Ended		1 Months Ended				12 Months Ended
	Jul. 31, 2013	Sep. 30, 2013	Sep. 30, 2012	Oct. 31, 2013 Subsequent Event	Jul. 31, 2012 Deposit into Litigation Escrow	Mar. 31, 2012 Deposit into Litigation Escrow	Dec. 31, 2011 Deposit into Litigation Escrow	Sep. 30, 2013 Class C common stock Accelerated Share Repurchase Program Aggregate
Class of Stock [Line Items]
Share repurchase plan, authorized amount	$ 1,500,000,000			$ 5,000,000,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount		251,000,000
Deposits into litigation escrow account			1,715,000,000		150,000,000	0	1,565,000,000
Shares of class C common stock released from transfer restrictions, converted to class A common stock								125
Dividends, per share amount declared				$ 0.40
Dividends, paid		$ 864,000,000
Dividends, paid per share		$ 0.33