Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Debt securities:
Less than 1 year	[1]	$ 423
1-5 years	[1]	6,078
5-10 years	[1]	19,333
Over 10 years	[1]	1,450
Equity securities		702
Available-for-sale and other securities, Amortized Cost		27,986	$ 21,677
Debt securities:
Less than 1 year	[1]	431
1-5 years	[1]	6,347
5-10 years	[1]	19,836
Over 10 years	[1]	1,481
Equity securities		704
Available-for-sale and other securities, fair value	[2]	28,799	22,408
Debt securities:
Less than 1 year	[1]	99
1-5 years	[1]	41
5-10 years	[1]	15
Over 10 years	[1]	2
Held-to-maturity securities, amortized cost	[3]	157	187
Debt securities:
Under 1 year	[1]	99
1-5 years	[1]	41
5-10 years	[1]	15
Over 10 years	[1]	2
Held-to-maturity securities, fair value		$ 157	$ 187

[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 $27,986 and $21,677 at September 30, 2015 and December 31, 2014, respectively.

[3] Fair value of $157 and $187 at September 30, 2015 and December 31, 2014, respectively.