Long-Term Debt - Textual (Detail) (USD $)	1 Months Ended
	May 31, 2012 Y	Sep. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Aggregate principle amount of senior unsecured notes		$ 17,571,000,000	$ 15,525,000,000
Available borrowing capacity under credit facility	4,000,000,000
Term of credit facility	5
Senior Unsecured Note [Member]
Debt Instrument [Line Items]
Aggregate principle amount of senior unsecured notes		2,500,000,000
Senior Unsecured Notes Due 2018 [Member]
Debt Instrument [Line Items]
Aggregate principle amount of senior unsecured notes		1,000,000,000
Stated interest rate of senior unsecured notes		1.10%
Senior Unsecured Notes Due 2022 [Member]
Debt Instrument [Line Items]
Aggregate principle amount of senior unsecured notes		1,000,000,000
Stated interest rate of senior unsecured notes		2.40%
Senior Unsecured Notes Due 2042 [Member]
Debt Instrument [Line Items]
Aggregate principle amount of senior unsecured notes		$ 500,000,000
Stated interest rate of senior unsecured notes		3.60%