Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Debt securities:
Less than 1 year	$ 219	[1]
1-5 years	8,564	[1]
5-10 years	14,641	[1]
Over 10 years	1,352	[1]
Equity securities	699
Available-for-sale and other securities, Amortized Cost	25,475		21,677
Debt securities:
Less than 1 year	222	[1]
1-5 years	8,982	[1]
5-10 years	15,101	[1]
Over 10 years	1,402	[1]
Equity securities	702
Available-for-sale and other securities, fair value	26,409	[2]	22,408	[2]
Debt securities:
Less than 1 year	112	[1]
1-5 years	47	[1]
5-10 years	16	[1]
Over 10 years	2	[1]
Held-to-maturity securities, amortized cost	177	[3]	187	[3]
Debt securities:
Under 1 year	112	[1]
1-5 years	47	[1]
5-10 years	16	[1]
Over 10 years	2	[1]
Held-to-maturity securities, fair value	$ 177		$ 187

[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 $25,475 and $21,677 at March 31, 2015 and December 31, 2014, respectively.

[3] Fair value of $177 and $187 at March 31, 2015 and December 31, 2014, respectively.