Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Derivative [Line Items]
Fair value hedges which increase (decrease) the carrying amount of debt		$ (3,000,000)	$ 1,000,000	$ (9,000,000)
Amortized of basis adjustments related to fair value hedge relationships	3,000,000	3,000,000	10,000,000	9,000,000
Total accumulated unamortized increase in fair value of hedge	37,000,000		37,000,000		49,000,000
Increases (decreases) in fair value hedges is available for sale of securities	38,000,000	44,000,000	(563,000,000)	231,000,000
Increase in accumulated unamortized adjustments for fair value hedges as available-for-sale securities	161,000,000		161,000,000		836,000,000
Cash flow hedge relationships extend or mature	July 2036		July 2036
Losses Related to cash flow hedge were amortized to earnings from accumulated other comprehensive income (loss)	2,000,000	4,000,000	9,000,000	12,000,000
Next twelve months, reclassification of remaining losses to earnings resulting from cash flow hedges			6,000,000
Aggregate fair value of all derivative instruments with credit-risk-related contingent	5,900,000,000		5,900,000,000		8,700,000,000
Collateral already posted aggregate fair value	5,300,000,000		5,300,000,000		7,900,000,000
Additional collateral aggregate fair value on return swap	15,000,000		15,000,000
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)	$ 2,000,000	$ 4,000,000	$ 9,000,000	$ 12,000,000