Investment Securities (Maturities of Securities Available for Sale) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Available for sale securities, fair value
Within 1 year	$ 9,348
After 1 year through 5 years	36,321
After 5 years through 10 years	80,173
After 10 years	251,126
Fair Value	376,968	$ 337,400
Available for sale securities, amortized cost
Within 1 year	9,311
After 1 year through 5 years	35,239
After 5 years through 10 years	79,456
After 10 years	251,299
Amortized Cost	375,305	330,248
U.S. agency mortgage-backed securities [Member]
Available for sale securities, fair value
Within 1 year	3,353
After 1 year through 5 years	21,031
After 5 years through 10 years	67,278
After 10 years	239,652
Fair Value	331,314	290,353
Available for sale securities, amortized cost
Amortized Cost	329,953	283,911
Asset-backed securities [Member]
Available for sale securities, fair value
Within 1 year	0
After 1 year through 5 years	5,075
After 5 years through 10 years	2,912
After 10 years	9,641
Fair Value	17,628	18,898
Available for sale securities, amortized cost
Amortized Cost	17,550	18,808
Corporate debt securities [Member]
Available for sale securities, fair value
Within 1 year	1,621
After 1 year through 5 years	6,815
After 5 years through 10 years	4,163
After 10 years	0
Fair Value	12,599	12,796
Available for sale securities, amortized cost
Amortized Cost	12,453	12,408
U.S. Treasury securities [Member]
Available for sale securities, fair value
Within 1 year	4,051
After 1 year through 5 years	2,576
After 5 years through 10 years	4,850
After 10 years	0
Fair Value	11,477	10,656
Available for sale securities, amortized cost
Amortized Cost	11,518	10,631
U.S. state and municipal securities [Member]
Available for sale securities, fair value
Within 1 year	23
After 1 year through 5 years	125
After 5 years through 10 years	970
After 10 years	584
Fair Value	1,702	1,697
Available for sale securities, amortized cost
Amortized Cost	1,617	1,544
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	1,223
Fair Value	1,223	1,265
Available for sale securities, amortized cost
Amortized Cost	1,192	1,213
Certificates of deposit [Member]
Available for sale securities, fair value
Within 1 year	300
After 1 year through 5 years	699
After 5 years through 10 years	0
After 10 years	0
Fair Value	999	300
Available for sale securities, amortized cost
Amortized Cost	1,000	300
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	26
Fair Value	26	22
Available for sale securities, amortized cost
Amortized Cost	$ 22	$ 22

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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