Securities (Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Debt securities:
Less than 1 year	[1]	$ 234
1-5 years	[1]	8,664
5-10 years	[1]	17,352
Over 10 years	[1]	5,368
Other securities		612
Available-for-sale debt securities, amortized cost		32,230	$ 31,577
Debt securities:
Less than 1 year	[1]	225
1-5 years	[1]	8,562
5-10 years	[1]	17,135
Over 10 years	[1]	5,285
Other securities		612
Available-for-sale debt and other securities, fair value	[2]	31,819	31,751
Debt securities:
Less than 1 year	[1]	5
1-5 years	[1]	15
5-10 years	[1]	1
Over 10 years	[1]	2
Other securities		0
Held-to-maturity securities, amortized cost	[3]	23	24
Debt securities:
Under 1 year	[1]	5
1-5 years	[1]	15
5-10 years	[1]	1
Over 10 years	[1]	2
Other securities		0
Held-to-maturity securities, fair value		$ 23	$ 24

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

[2] Amortized cost of $ 32,230 and $ 31,577 at March 31, 2018 and December 31, 2017 , respectively.

[3] Fair value of $ 23 and $ 24 at March 31, 2018 and December 31, 2017 , respectively.