Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Debt securities:
Total	$ 20,393		$ 18,409
Debt securities:
Fair Value	20,749	[1]	18,597	[1]
Debt securities:
Total	195	[2]	208	[2]
Debt securities:
Fair Value	195		208
Available-for-sale Securities
Debt securities:
Under 1 year	92	[3]
1-5 years	3,626	[3]
5-10 years	12,430	[3]
Over 10 years	3,532	[3]
Other securities	713	[3]
Total	20,393	[3]	18,409
Debt securities:
Under 1 year	95	[3]
1-5 years	3,814	[3]
5-10 years	12,507	[3]
Over 10 years	3,615	[3]
Other securities	718	[3]
Fair Value	20,749	[3]	18,597
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	16	[3]
1-5 years	160	[3]
5-10 years	17	[3]
Over 10 years	2	[3]
Total	195	[3]	208
Debt securities:
Under 1 year	16	[3]
1-5 years	160	[3]
5-10 years	17	[3]
Over 10 years	2	[3]
Fair Value	$ 195	[3]	$ 208

[1] Amortized cost of $20,393 and $18,409 at March 31, 2014 and December 31, 2013, respectively.

[2] Fair value of $195 and $208 at March 31, 2014 and December 31, 2013, respectively.

[3] Actual maturities may differ from contractual maturities when there exists a right to call or prepay obligations with or without call or prepayment penalties.