Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Debt securities:
Under 1 year	$ 555	[1]
1-5 years	8,865	[1]
5-10 years	2,223	[1]
Over 10 years	1,895	[1]
Other securities	1,033
Total	14,571		14,614
Debt securities:
Under 1 year	566	[1]
1-5 years	9,356	[1]
5-10 years	2,280	[1]
Over 10 years	1,969	[1]
Other securities	1,036
Fair Value	15,207	[2]	15,362	[2]
Debt securities:
Under 1 year	73	[1]
1-5 years	185	[1]
5-10 years	20	[1]
Over 10 years	6	[1]
Total	284	[3]	322	[3]
Debt securities:
Under 1 year	73	[1]
1-5 years	185	[1]
5-10 years	20	[1]
Over 10 years	6	[1]
Fair Value	$ 284		$ 322

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

[2] Amortized cost of $14,571 and $14,614 at December 31, 2012 and 2011, respectively.

[3] Fair value of $284 and $322 at December 31, 2012 and 2011, respectively.