Investment Securities (Maturities of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions		Dec. 31, 2020	Dec. 31, 2019
Available for sale securities, fair value
Within 1 year		$ 16,146
After 1 year through 5 years		36,540
After 5 years through 10 years		70,971
After 10 years		213,743
Fair Value	[1]	337,400	$ 61,422
Available for sale securities, amortized cost
Within 1 year		16,080
After 1 year through 5 years		35,119
After 5 years through 10 years		68,080
After 10 years		210,969
Amortized Cost		$ 330,248	61,155
Weighted-average yield
Within 1 year		1.01%
After 1 year through 5 years		2.09%
After 1 year through 5 years		1.81%
After 10 years		1.10%
Total		1.35%
U.S. agency mortgage-backed securities [Member]
Available for sale securities, fair value
Within 1 year		$ 1,758
After 1 year through 5 years		22,392
After 5 years through 10 years		63,400
After 10 years		202,803
Fair Value		290,353	46,155
Available for sale securities, amortized cost
Amortized Cost		283,911	45,964
Asset-backed securities [Member]
Available for sale securities, fair value
Within 1 year		15
After 1 year through 5 years		5,975
After 5 years through 10 years		4,012
After 10 years		8,896
Fair Value		18,898	4,987
Available for sale securities, amortized cost
Amortized Cost		18,808	4,970
Corporate debt securities [Member]
Available for sale securities, fair value
Within 1 year		3,632
After 1 year through 5 years		6,429
After 5 years through 10 years		2,735
After 10 years		0
Fair Value		12,796	5,484
Available for sale securities, amortized cost
Amortized Cost		12,408	5,427
U.S. Treasury securities [Member]
Available for sale securities, fair value
Within 1 year		10,316
After 1 year through 5 years		340
After 5 years through 10 years		0
After 10 years		0
Fair Value		10,656	3,384
Available for sale securities, amortized cost
Amortized Cost		10,631	3,387
U.S. state and municipal securities [Member]
Available for sale securities, fair value
Within 1 year		0
After 1 year through 5 years		116
After 5 years through 10 years		824
After 10 years		757
Fair Value		1,697
Available for sale securities, amortized cost
Amortized Cost		1,544
Foreign government agency securities [Member]
Available for sale securities, fair value
Within 1 year		125
After 1 year through 5 years		1,288
After 5 years through 10 years		0
After 10 years		0
Fair Value		1,413
Available for sale securities, amortized cost
Amortized Cost		1,411
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities, fair value
Within 1 year		0
After 1 year through 5 years		0
After 5 years through 10 years		0
After 10 years		1,265
Fair Value		1,265	13
Available for sale securities, amortized cost
Amortized Cost		1,213	13
Certificates of deposit [Member]
Available for sale securities, fair value
Within 1 year		300
After 1 year through 5 years		0
After 5 years through 10 years		0
After 10 years		0
Fair Value		300	1,004
Available for sale securities, amortized cost
Amortized Cost		300	$ 1,000
Other [Member]
Available for sale securities, fair value
Within 1 year		0
After 1 year through 5 years		0
After 5 years through 10 years		0
After 10 years		22
Fair Value		22
Available for sale securities, amortized cost
Amortized Cost		$ 22

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.