Securities - Amortized Cost and Fair Value of Available-for-Sale and Held-to-Maturity Securities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Debt securities:
Less than 1 year	$ 197
1-5 years	13,391
5-10 years	16,568
Over 10 years	4,931
Other securities	575
Available-for-sale debt securities, amortized cost	35,662	$ 33,128
Debt securities:
Less than 1 year	207
1-5 years	13,817
5-10 years	17,390
Over 10 years	5,189
Other securities	575
Available-for-sale debt and other securities, fair value	37,178	32,830
Debt securities:
Less than 1 year	2
1-5 years	14
5-10 years	0
Over 10 years	2
Other securities	0
Held-to-maturity securities, amortized cost	18	18
Debt securities:
Under 1 year	2
1-5 years	14
5-10 years	0
Over 10 years	2
Other securities	0
Held-to-maturity securities, fair value	$ 18	$ 18