Securities (Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Debt securities:
Less than 1 year	[1]	$ 140
1-5 years	[1]	9,695
5-10 years	[1]	17,592
Over 10 years	[1]	3,538
Equity securities		679
Available-for-sale and other securities, Amortized Cost		31,644	$ 31,024
Debt securities:
Less than 1 year	[1]	141
1-5 years	[1]	9,707
5-10 years	[1]	17,734
Over 10 years	[1]	3,557
Equity securities		681
Available-for-sale and other securities, fair value	[2]	31,820	31,183
Debt securities:
Less than 1 year	[1]	5
1-5 years	[1]	13
5-10 years	[1]	4
Over 10 years	[1]	2
Equity securities		0
Held-to-maturity securities, amortized cost	[3]	24	26
Debt securities:
Less than 1 year	[1]	5
1-5 years	[1]	13
5-10 years	[1]	4
Over 10 years	[1]	2
Equity securities		0
Held-to-maturity securities, fair value		$ 24	$ 26

[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 $ 31,644 and $ 31,024 at December 31, 2017 and 2016 , respectively.

[3] Fair value of $ 24 and $ 26 at December 31, 2017 and 2016 , respectively.