Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Debt securities:
Total	$ 22,184		$ 18,409
Debt securities:
Available for sale securities	22,814	[1]	18,597	[1]
Debt securities:
Total	194	[2]	208	[2]
Debt securities:
Held-to-maturity securities	194		208
Available-for-sale Securities
Debt securities:
Under 1 year	114	[3]
1-5 years	3,476	[3]
5-10 years	12,479	[3]
Over 10 years	5,391	[3]
Other securities	724	[3]
Total	22,184	[3]	18,409
Debt securities:
Under 1 year	116	[3]
1-5 years	3,673	[3]
5-10 years	12,763	[3]
Over 10 years	5,532	[3]
Other securities	730	[3]
Available for sale securities	22,814	[3]	18,597
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	35	[3]
1-5 years	140	[3]
5-10 years	17	[3]
Over 10 years	2	[3]
Total	194	[3]	208
Debt securities:
Under 1 year	35	[3]
1-5 years	140	[3]
5-10 years	17	[3]
Over 10 years	2	[3]
Held-to-maturity securities	$ 194	[3]	$ 208

[1] Amortized cost of $22,184 and $18,409 at June 30, 2014 and December 31, 2013, respectively.

[2] Fair value of $194 and $208 at June 30, 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.