Investment Securities (Amortized Cost and Fair Value of Available-for-Sale Debt and Held-to-Maturity Securities) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt securities:
Less than 1 year	$ 36
1-5 years	13,751
5-10 years	15,746
Over 10 years	6,279
Other securities	616
Available-for-sale debt securities, Amortized Cost	36,428	$ 34,966
Debt securities:
Less than 1 year	37
1-5 years	14,523
5-10 years	16,868
Over 10 years	6,601
Other securities	616
Available-for-sale debt and other securities, fair value	38,645	36,028
Debt securities:
Less than 1 year	15
1-5 years	0
5-10 years	0
Over 10 years	2
Other securities	0
Held-to-maturity securities, amortized cost	17	17
Debt securities:
Less than 1 year	15
1-5 years	0
5-10 years	0
Over 10 years	2
Other securities	0
Held-to-maturity securities, fair value	$ 17	$ 17