Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011		Jun. 30, 2011
Debt securities:
Fair Value	$ 15,552	[1]	$ 15,362	[1]	$ 15,502	[1]
Debt securities:
Total	305	[2]	322	[2]	344	[2]
Available-for-sale Securities
Debt securities:
Under 1 year	669	[3]
1-5 years	9,525	[3]
5-10 years	1,814	[3]
Over 10 years	1,579	[3]
Other securities	1,231	[3]
Total	14,818		14,614		14,889
Debt securities:
Under 1 year	686	[3]
1-5 years	10,121	[3]
5-10 years	1,888	[3]
Over 10 years	1,623	[3]
Other securities	1,234	[3]
Fair Value	15,552		15,362		15,502
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	21	[3]
1-5 years	253	[3]
5-10 years	20	[3]
Over 10 years	11	[3]
Total	305		322		344
Debt securities:
Under 1 year	21	[3]
1-5 years	253	[3]
5-10 years	20	[3]
Over 10 years	11	[3]
Fair Value	$ 305		$ 322		$ 344

[1] Amortized cost of $14,818, $14,614 and $14,889 at June 30, 2012, December 31, 2011 and June 30, 2011, respectively.

[2] Fair value of $305, $322 and $344 at June 30, 2012, December 31, 2011 and June 30, 2011, respectively.

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