Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Net gain (loss) in fair value of Derivative in qualifying fair value hedge	$ 17,000,000	$ (30,000,000)	$ 12,000,000	$ (20,000,000)
Fair value hedges which decreased the carrying amount of debt		1,000,000	(1,000,000)	6,000,000
Amortized of basis adjustments related to fair value hedge relationships	3,000,000	3,000,000	7,000,000	6,000,000
Total accumulated unamortized increase in fair value of hedge	41,000,000		41,000,000		49,000,000
Increases in fair value hedges is available for sale of securities	445,000,000	481,000,000	600,000,000	187,000,000
Increase in accumulated unamortized adjustments for fair value hedges as available-for-sale securities	154,000,000		154,000,000		836,000,000
Cash flow hedge relationships extend or mature	July 2036		July 2036
Next twelve months, reclassification of remaining losses to earnings resulting from cash flow hedges			10,000,000
Aggregate fair value of all derivative instruments with credit-risk-related contingent	7,100,000,000		7,100,000,000		8,700,000,000
Collateral already posted aggregate fair value	5,600,000,000		5,600,000,000		7,900,000,000
Additional collateral aggregate fair value on return swap	17,000,000		17,000,000
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Losses Related to cash flow hedge were amortized to earnings from accumulated other comprehensive income (loss)	$ 3,000,000	$ 4,000,000	$ 7,000,000	$ 8,000,000