Securities (Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Debt securities:
Less than 1 year	[1]	$ 14
1-5 years	[1]	9,080
5-10 years	[1]	18,305
Over 10 years	[1]	4,757
Other securities		551
Available-for-sale debt securities, amortized cost		32,707	$ 31,577
Debt securities:
Less than 1 year	[1]	14
1-5 years	[1]	8,882
5-10 years	[1]	17,771
Over 10 years	[1]	4,590
Other securities		551
Available-for-sale debt and other securities, fair value	[2]	31,808	31,751
Debt securities:
Less than 1 year	[1]	0
1-5 years	[1]	16
5-10 years	[1]	0
Over 10 years	[1]	2
Other securities		0
Held-to-maturity securities, amortized cost	[3]	18	24
Debt securities:
Under 1 year	[1]	0
1-5 years	[1]	16
5-10 years	[1]	0
Over 10 years	[1]	2
Other securities		0
Held-to-maturity securities, fair value		$ 18	$ 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 $ 32,707 and $ 31,577 at September 30, 2018 and December 31, 2017 , respectively.

[3] Fair value of $ 18 and $ 24 at September 30, 2018 and December 31, 2017 , respectively.