Fair Value Option - Components of Gain (Loss) on Debt Designated at Fair Value and Related Derivatives (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Mark-to-market on debt designated at fair value :
Interest rate component	$ 168	[1]	$ 314	[1]	$ 166	[1]
Credit risk component	27	[1]	(71)	[1]	(758)	[1]
Total mark-to-market on debt designated at fair value	195	[1]	243	[1]	(592)	[1]
Mark-to-market on the related derivatives	(254)	[1]	(333)	[1]	(260)	[1]
Net realized gains on the related derivatives	267		318		403
Gain (loss) on debt designated at fair value and related derivatives	$ 208		$ 228		$ (449)

[1] Mark-to-market on debt designated at fair value and related derivatives excludes market value changes due to fluctuations in foreign currency exchange rates. Foreign currency translation gains (losses) recorded in derivative related income (expense) associated with debt designated at fair value was a gain of $391 million, a loss of $73 million and a loss of $35 million during 2014, 2013 and 2012, respectively. Offsetting gains (losses) recorded in derivative related income (expense) associated with the related derivatives was a loss of $391 million, a gain of $73 million and a gain of $35 million during 2014, 2013 and 2012, respectively.