Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Debt securities:
Total	$ 15,793		$ 14,571
Debt securities:
Fair Value	16,187	[1]	15,207	[1]
Debt securities:
Total	274	[2]	284	[2]
Debt securities:
Fair Value	274		284
Available-for-sale Securities
Debt securities:
Under 1 year	771
1-5 years	4,521
5-10 years	6,656
Over 10 years	2,867
Other securities	978
Total	15,793		14,571
Debt securities:
Under 1 year	764
1-5 years	4,755
5-10 years	6,755
Over 10 years	2,926
Other securities	987
Fair Value	16,187		15,207
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	80
1-5 years	173
5-10 years	20
Over 10 years	1
Total	274		284
Debt securities:
Under 1 year	80
1-5 years	173
5-10 years	20
Over 10 years	1
Fair Value	$ 274		$ 284

[1] Amortized cost of $15,793 and $14,571 at June 30, 2013 and December 31, 2012, respectively.

[2] Fair value of $274 and $284 at June 30, 2013 and December 31, 2012, respectively.