Derivative Financial Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Derivative [Line Items]
Fair value hedges which increase (decrease) the carrying amount of debt (less than $1 million for the 3 months ended June 30, 2014 and June 30, 2013)	$ (1)	$ 1	$ (1)	$ 1
Amortization of basis adjustments related to fair value hedge relationships	2	3	5	7
Increase (decrease) in accumulated unamortized adjustments for carrying amount of debt	27		27		33
Increase (decrease) in basis adjustment for active fair value hedges of available for sale securities	162	(445)	338	(600)
Increase (decrease) In accumulated unamortized adjustments for fair value hedges as available for sale securities	281		281		(84)
Next twelve months, reclassification of remaining losses to earnings resulting from cash flow hedges			9
Aggregate fair value of all derivative instruments with credit-risk-related contingent	4,701		4,701		5,614
Collateral already posted aggregate fair value	3,837		3,837		5,059
Additional collateral aggregate fair value on return swap	5		5
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)	$ (2)	$ (3)	$ (3)	$ (7)