Investment Securities (Amortized Cost and Fair Value of Available-for-Sale Debt and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt securities:
Less than 1 year	$ 195
1-5 years	10,983
5-10 years	17,566
Over 10 years	5,666
Other securities	556
Available-for-sale debt securities, Amortized Cost	34,966	$ 33,128
Debt securities:
Less than 1 year	200
1-5 years	11,288
5-10 years	18,173
Over 10 years	5,811
Other securities	556
Available-for-sale debt and other securities, fair value	36,028	32,830
Debt securities:
Less than 1 year	5
1-5 years	10
5-10 years	0
Over 10 years	2
Other securities	0
Held-to-maturity securities, amortized cost	17	18
Debt securities:
Less than 1 year	5
1-5 years	10
5-10 years	0
Over 10 years	2
Other securities	0
Held-to-maturity securities, fair value	$ 17	$ 18