Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Net gain (loss) in fair value of Derivative in qualifying fair value hedge	$ (4,000,000)	$ 11,000,000
Fair value hedges which decreased the carrying amount of debt	1,000,000	4,000,000
Amortized of basis adjustments related to fair value hedge relationships	3,000,000	3,000,000
Total accumulated unamortized increase in fair value of hedge	45,000,000		49,000,000
Increases in fair value hedges is available for sale of securities	(155,000,000)	(294,000,000)
Increase in accumulated unamortized adjustments for fair value hedges as available-for-sale securities	631,000,000		836,000,000
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)	4,000,000	4,000,000
Next twelve months, reclassification of remaining losses to earnings resulting from cash flow hedges	11,000,000
Aggregate fair value of all derivative instruments with credit-risk-related contingent	8,800,000,000		8,700,000,000
Collateral already posted aggregate fair value	7,000,000,000		7,900,000,000
Additional collateral aggregate fair value on return swap	$ 0