Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Debt securities:
Under 1 year	$ 160	[1]
1-5 years	4,237	[1]
5-10 years	14,718	[1]
Over 10 years	2,557	[1]
Equity securities	720
Available-for-sale and other securities, Amortized Cost	22,392		18,409
Debt securities:
Under 1 year	162	[1]
1-5 years	4,426	[1]
5-10 years	14,965	[1]
Over 10 years	2,633	[1]
Equity securities	726
Available-for-sale and other securities, fair value	22,912	[2]	18,597	[2]
Debt securities:
Under 1 year	37	[1]
1-5 years	135	[1]
5-10 years	17	[1]
Over 10 years	2	[1]
Held-to-maturity securities, amortized cost	191	[3]	208	[3]
Debt securities:
Under 1 year	37	[1]
1-5 years	135	[1]
5-10 years	17	[1]
Over 10 years	2	[1]
Held-to-maturity securities, fair value	$ 191		$ 208

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

[2] Amortized cost of $22,392 and $18,409 at September 30, 2014 and December 31, 2013, respectively.

[3] Fair value of $191 and $208 at September 30, 2014 and December 31, 2013, respectively.