Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Debt securities:
Total	$ 14,652		$ 14,571
Debt securities:
Fair Value	15,263	[1]	15,207	[1]
Debt securities:
Total	283	[2]	284	[2]
Debt securities:
Fair Value	283		284
Available-for-sale Securities
Debt securities:
Under 1 year	610
1-5 years	8,717
5-10 years	2,146
Over 10 years	2,120
Other securities	1,059
Total	14,652		14,571
Debt securities:
Under 1 year	623
1-5 years	9,150
5-10 years	2,220
Over 10 years	2,204
Other securities	1,066
Fair Value	15,263		15,207
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	85
1-5 years	172
5-10 years	21
Over 10 years	5
Total	283		284
Debt securities:
Under 1 year	85
1-5 years	172
5-10 years	21
Over 10 years	5
Fair Value	$ 283		$ 284

[1] Amortized cost of $14,652 and $14,571 at March 31, 2013 and December 31, 2012, respectively.

[2] Fair value of $283 and $284 at March 31, 2013 and December 31, 2012, respectively.