Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012
Debt securities:
Total	$ 17,665		$ 14,571
Debt securities:
Fair Value	18,080	[1]	15,207	[1]
Debt securities:
Total	265	[2]	284	[2]
Debt securities:
Fair Value	265		284
Available-for-sale Securities
Debt securities:
Under 1 year	282
1-5 years	4,984
5-10 years	7,806
Over 10 years	3,601
Other securities	992
Total	17,665		14,571
Debt securities:
Under 1 year	291
1-5 years	5,215
5-10 years	7,906
Over 10 years	3,664
Other securities	1,004
Fair Value	18,080		15,207
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	72
1-5 years	174
5-10 years	18
Over 10 years	1
Total	265		284
Debt securities:
Under 1 year	72
1-5 years	174
5-10 years	18
Over 10 years	1
Fair Value	$ 265		$ 284

[1] Amortized cost of $17,665 and $14,571 at September 30, 2013 and December 31, 2012, respectively.

[2] Fair value of $265 and $284 at September 30, 2013 and December 31, 2012, respectively.