Securities - Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Debt securities:
Less than 1 year	$ 213
1-5 years	11,842
5-10 years	17,347
Over 10 years	4,783
Other securities	546
Available-for-sale debt securities, amortized cost	34,731	$ 33,128
Debt securities:
Less than 1 year	220
1-5 years	12,161
5-10 years	17,899
Over 10 years	4,927
Other securities	546
Available-for-sale debt and other securities, fair value	35,753	32,830
Debt securities:
Less than 1 year	2
1-5 years	14
5-10 years	0
Over 10 years	5
Other securities	0
Held-to-maturity securities, amortized cost	21	18
Debt securities:
Under 1 year	2
1-5 years	14
5-10 years	0
Over 10 years	5
Other securities	0
Held-to-maturity securities, fair value	$ 21	$ 18