Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Detail) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Debt securities:
Less than 1 year	[1]	$ 835
1-5 years	[1]	9,003
5-10 years	[1]	16,480
Over 10 years	[1]	1,817
Equity securities		703
Available-for-sale and other securities, Amortized Cost		28,838	$ 28,678
Debt securities:
Less than 1 year	[1]	857
1-5 years	[1]	9,329
5-10 years	[1]	17,146
Over 10 years	[1]	1,855
Equity securities		704
Available-for-sale and other securities, fair value	[2]	29,891	29,044
Debt securities:
Less than 1 year	[1]	37
1-5 years	[1]	12
5-10 years	[1]	13
Over 10 years	[1]	2
Held-to-maturity securities, amortized cost	[3]	64	70
Debt securities:
Under 1 year	[1]	37
1-5 years	[1]	12
5-10 years	[1]	13
Over 10 years	[1]	2
Held-to-maturity securities, fair value		$ 64	$ 70

[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 $28,838 and $28,678 at March 31, 2016 and December 31, 2015, respectively.

[3] Fair value of $64 and $70 at March 31, 2016 and December 31, 2015, respectively.