Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Derivative [Line Items]
Fair value hedges which increase (decrease) the carrying amount of debt	$ 1	$ (1)
Amortization of basis adjustments related to fair value hedge relationships	3	3
Total accumulated unamortized increase in fair value of hedge	29		33
Increases (decreases) in fair value hedges is available for sale of securities	176	(155)
Increase in accumulated unamortized adjustments for fair value hedges as available-for-sale securities	113		84
Cash flow hedge relationships extend or mature	July 2036
Income (loss) related to cash flow hedge were amortized to earnings from accumulated other comprehensive income (loss)	(1)	(4)
Next twelve months, reclassification of remaining losses to earnings resulting from cash flow hedges	8
Aggregate fair value of all derivative instruments with credit-risk-related contingent	4,838		5,614
Collateral already posted aggregate fair value	4,052		5,059
Additional collateral aggregate fair value on return swap	6
Cash Flow Hedging [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Income (loss) related to cash flow hedge were amortized to earnings from accumulated other comprehensive income (loss)	$ (1)	$ (4)