Securities (Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Debt securities:
Less than 1 year	[1]	$ 328
1-5 years	[1]	7,290
5-10 years	[1]	20,043
Over 10 years	[1]	2,666
Equity securities		697
Available-for-sale and other securities, Amortized Cost		31,024	$ 28,678
Debt securities:
Less than 1 year	[1]	332
1-5 years	[1]	7,347
5-10 years	[1]	20,146
Over 10 years	[1]	2,660
Equity securities		698
Available-for-sale and other securities, fair value	[2]	31,183	29,044
Debt securities:
Less than 1 year	[1]	2
1-5 years	[1]	11
5-10 years	[1]	12
Over 10 years	[1]	1
Equity securities		0
Held-to-maturity securities, amortized cost	[3]	26	70
Debt securities:
Less than 1 year	[1]	2
1-5 years	[1]	11
5-10 years	[1]	12
Over 10 years	[1]	1
Equity securities		0
Held-to-maturity securities, fair value		$ 26	$ 70

[1] (a) Actual maturities may differ from contractu al maturities when a right to call or prepay obligations exists with or without call or prepayment penalties.

[2] Amortized cost of $ 31,024 and $ 28,678 at December 31, 2016 and 2015 , respectively.

[3] Fair value of $ 26 and $ 70 at December 31, 2016 and 2015 , respectively.