Derivative Financial Instruments - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Disclosure Derivative Financial Instruments Additional Information [Abstract]
Net gain (loss) in fair value of Derivative in qualifying fair value hedge	$ (13,000,000)	$ (74,000,000)
Fair value hedges which decreased the carrying amount of debt	(8,000,000)	17,000,000
Amortized of basis adjustments related to fair value hedge relationships	12,000,000	11,000,000
Total accumulated unamortized increase in fair value of hedge	49,000,000	53,000,000
Increases in fair value hedges is available for sale of securities	130,000,000	1,000,000,000
Increase in accumulated unamortized adjustments for fair value hedges as available-for-sale securities	836,000,000	1,100,000,000
Cash flow hedge relationships extend or mature	July 2036
Losses Related to cash flow hedge were amortized to earnings from accumulated other comprehensive income (loss)	17,000,000	13,000,000
Next twelve months, reclassification of remaining losses to earnings resulting from cash flow hedges	12,000,000
Aggregate fair value of all derivative instruments with credit-risk-related contingent	8,700,000,000	10,300,000,000
Collateral already posted aggregate fair value	7,900,000,000	8,500,000,000
Additional collateral aggregate fair value on return swap	$ 33,000,000