Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011
Debt securities:
Total	$ 15,341		$ 14,614		$ 14,707
Debt securities:
Fair Value	16,093	[1]	15,362	[1]	15,135	[1]
Debt securities:
Total	321	[2]	322	[2]	346	[2]
Debt securities:
Fair Value	321		322		346
Available-for-sale Securities
Debt securities:
Under 1 year	612	[3]
1-5 years	10,473	[3]
5-10 years	1,996	[3]
Over 10 years	1,111	[3]
Other securities	1,149	[3]
Total	15,341		14,614		14,707
Debt securities:
Under 1 year	629	[3]
1-5 years	11,044	[3]
5-10 years	2,125	[3]
Over 10 years	1,144	[3]
Other securities	1,151	[3]
Fair Value	16,093		15,362		15,135
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	36	[3]
1-5 years	254	[3]
5-10 years	16	[3]
Over 10 years	15	[3]
Total	321		322		346
Debt securities:
Under 1 year	36	[3]
1-5 years	254	[3]
5-10 years	16	[3]
Over 10 years	15	[3]
Fair Value	$ 321		$ 322		$ 346

[1] Amortized cost of $15,341, $14,614 and $14,707 at March 31, 2012, December 31, 2011 and March 31, 2011, respectively.

[2] Fair value of $321, $322 and $346 at March 31, 2012, December 31, 2011 and March 31, 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.