Investment Securities (Maturities of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available for sale securities, fair value
Within 1 year	$ 7,691
After 1 year through 5 years	13,931
After 5 years through 10 years	12,606
After 10 years	20,420
Fair Value	54,648	$ 66,578
Available for sale securities, amortized cost
Within 1 year	7,692
After 1 year through 5 years	13,863
After 5 years through 10 years	12,588
After 10 years	20,221
Amortized Cost	54,364	66,735
Held to maturity securities, fair value
Within 1 year	1,204
After 1 year through 5 years	21,376
After 5 years through 10 years	44,162
After 10 years	72,752
Fair Value	139,494	142,038
Held to maturity securities, amortized cost
Within 1 year	1,203
After 1 year through 5 years	21,138
After 5 years through 10 years	43,371
After 10 years	72,614
Amortized Cost	138,326	144,009
U.S. agency mortgage-backed securities [Member]
Available for sale securities, fair value
Within 1 year	35
After 1 year through 5 years	1,234
After 5 years through 10 years	11,605
After 10 years	20,113
Fair Value	32,987	25,556
Available for sale securities, amortized cost
Amortized Cost	32,773	25,594
Held to maturity securities, fair value
Within 1 year	156
After 1 year through 5 years	15,464
After 5 years through 10 years	34,066
After 10 years	63,847
Fair Value	113,533	116,093
Held to maturity securities, amortized cost
Amortized Cost	112,570	118,064
U.S. Treasury securities [Member]
Available for sale securities, fair value
Within 1 year	4,432
After 1 year through 5 years	2,901
After 5 years through 10 years	0
After 10 years	0
Fair Value	7,333	18,302
Available for sale securities, amortized cost
Amortized Cost	7,352	18,410
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	0
After 5 years through 10 years	227
After 10 years	0
Fair Value	227	217
Held to maturity securities, amortized cost
Amortized Cost	223	223
Asset-backed securities [Member]
Available for sale securities, fair value
Within 1 year	0
After 1 year through 5 years	4,791
After 5 years through 10 years	1,001
After 10 years	293
Fair Value	6,085	10,085
Available for sale securities, amortized cost
Amortized Cost	6,055	10,086
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	2,300
After 5 years through 10 years	8,802
After 10 years	7,159
Fair Value	18,261	18,546
Held to maturity securities, amortized cost
Amortized Cost	18,218	18,502
Corporate debt securities [Member]
Available for sale securities, fair value
Within 1 year	1,631
After 1 year through 5 years	3,800
After 5 years through 10 years	0
After 10 years	0
Fair Value	5,431	7,467
Available for sale securities, amortized cost
Amortized Cost	5,378	7,477
Held to maturity securities, fair value
Within 1 year	847
After 1 year through 5 years	3,098
After 5 years through 10 years	688
After 10 years	0
Fair Value	4,633	4,432
Held to maturity securities, amortized cost
Amortized Cost	4,593	4,477
Certificates of deposit [Member]
Available for sale securities, fair value
Within 1 year	921
After 1 year through 5 years	1,205
After 5 years through 10 years	0
After 10 years	0
Fair Value	2,126	3,685
Available for sale securities, amortized cost
Amortized Cost	2,120	3,682
Held to maturity securities, fair value
Within 1 year	201
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	0
Fair Value	201	201
Held to maturity securities, amortized cost
Amortized Cost	200	200
U.S. agency notes [Member]
Available for sale securities, fair value
Within 1 year	250
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	0
Fair Value	250	898
Available for sale securities, amortized cost
Amortized Cost	250	900
U.S. state and municipal securities [Member]
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	98
After 5 years through 10 years	379
After 10 years	926
Fair Value	1,403	1,348
Held to maturity securities, amortized cost
Amortized Cost	1,310	1,327
Commercial paper [Member]
Available for sale securities, fair value
Within 1 year	422
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	0
Fair Value	422	522
Available for sale securities, amortized cost
Amortized Cost	422	522
Foreign government agency securities [Member]
Available for sale securities, fair value
Fair Value		49
Available for sale securities, amortized cost
Amortized Cost		50
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	50
After 5 years through 10 years	0
After 10 years	0
Fair Value	50	49
Held to maturity securities, amortized cost
Amortized Cost	50	50
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	14
Fair Value	14	14
Available for sale securities, amortized cost
Amortized Cost	14	14
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	366
After 5 years through 10 years	0
After 10 years	801
Fair Value	1,167	1,142
Held to maturity securities, amortized cost
Amortized Cost	1,143	1,156
Other [Member]
Held to maturity securities, fair value
Within 1 year	0
After 1 year through 5 years	0
After 5 years through 10 years	0
After 10 years	19
Fair Value	19	10
Held to maturity securities, amortized cost
Amortized Cost	$ 19	$ 10