Investment Securities - Amortized Cost and Fair Value of Available-for-Sale Debt and Held-to-Maturity Securities (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Available-for-Sale Debt and Other, Amortized Cost
Due in 1 year or less	$ 3,140
Due after 1 year through 5 years	17,036
Due after 5 years through 10 years	16,020
Due after 10 years	6,781
Other securities	777
Amortized Cost	43,754	$ 55,789
Available-for-Sale Debt and Other, Fair Value
Due in 1 year or less	3,117
Due after 1 year through 5 years	16,376
Due after 5 years through 10 years	14,120
Due after 10 years	6,006
Other securities	777
Fair Value	40,396	50,419
Held-to-Maturity, Amortized Cost
Due in 1 year or less	38
Due after 1 year through 5 years	3,071
Due after 5 years through 10 years	7,770
Due after 10 years	479
Other securities	0
Amortized Cost	11,358	2
Held-to-Maturity, Fair Value
Due in 1 year or less	38
Due after 1 year through 5 years	3,106
Due after 5 years through 10 years	7,908
Due after 10 years	502
Other securities	0
Fair Value	$ 11,554	$ 2