Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011
Debt securities:
Total	$ 14,641		$ 14,614		$ 15,427
Debt securities:
Fair Value	15,402	[1]	15,362	[1]	16,227	[1]
Debt securities:
Total	287	[2]	322	[2]	337	[2]
Debt securities:
Fair Value	287		322		337
Available-for-sale Securities
Debt securities:
Under 1 year	605	[3]
1-5 years	9,411	[3]
5-10 years	1,722	[3]
Over 10 years	1,825	[3]
Other securities	1,078	[3]
Total	14,641		14,614		15,427
Debt securities:
Under 1 year	619	[3]
1-5 years	10,003	[3]
5-10 years	1,812	[3]
Over 10 years	1,890	[3]
Other securities	1,078	[3]
Fair Value	15,402		15,362		16,227
Held-to-maturity Securities [Member]
Debt securities:
Under 1 year	18	[3]
1-5 years	239	[3]
5-10 years	20	[3]
Over 10 years	10	[3]
Total	287		322		337
Debt securities:
Under 1 year	18	[3]
1-5 years	239	[3]
5-10 years	20	[3]
Over 10 years	10	[3]
Fair Value	$ 287		$ 322		$ 337

[1] Amortized cost of $14,641, $14,614 and $15,427 at September 30, 2012, December 31, 2011 and September 30, 2011, respectively.

[2] Fair value of $287, $322 and $337 at September 30, 2012, December 31, 2011 and September 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.