Investment Securities (Available For Sale and Held to Maturity Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss) (Details) $ in Millions	Sep. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Available for sale securities:
Less than 12 months Fair Value	$ 13,352	$ 23,503
Less than 12 months Unrealized Losses	26	67
12 months or longer Fair Value	10,375	12,888
12 months or longer Unrealized Losses	39	162
Total Fair Value	23,727	36,391
Total Unrealized Losses	65	229
Held to maturity securities:
Less than 12 months Fair Value	19,892	39,327
Less than 12 months Unrealized Losses	72	290
12 months or longer Fair Value	21,807	58,794
12 months or longer Unrealized Losses	206	2,011
Total Fair Value	41,699	98,121
Total Unrealized Losses	278	2,301
Total securities with unrealized losses
Less than 12 months Fair Value	33,244	62,830
Less than 12 months Unrealized Losses	98	357
12 months or longer Fair Value	32,182	71,682
12 months or longer Unrealized Losses	245	2,173
Total Fair Value	65,426	134,512
Total Unrealized Losses	$ 343	$ 2,530
Number of available for sale securities in unrealized loss positions | security	343	441
Number of held to maturity securities in unrealized loss positions | security	625	1,524
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	$ 12,063	$ 9,529
Less than 12 months Unrealized Losses	24	32
12 months or longer Fair Value	6,317	4,257
12 months or longer Unrealized Losses	23	50
Total Fair Value	18,380	13,786
Total Unrealized Losses	47	82
Held to maturity securities:
Less than 12 months Fair Value	11,838	29,263
Less than 12 months Unrealized Losses	37	222
12 months or longer Fair Value	20,897	56,435
12 months or longer Unrealized Losses	201	1,966
Total Fair Value	32,735	85,698
Total Unrealized Losses	238	2,188
U.S. Treasury securities [Member]
Available for sale securities:
Less than 12 months Fair Value	377	4,951
Less than 12 months Unrealized Losses	0	6
12 months or longer Fair Value	3,161	7,037
12 months or longer Unrealized Losses	10	102
Total Fair Value	3,538	11,988
Total Unrealized Losses	10	108
Held to maturity securities:
Less than 12 months Fair Value		0
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		218
12 months or longer Unrealized Losses		6
Total Fair Value		218
Total Unrealized Losses		6
Asset-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	763	4,050
Less than 12 months Unrealized Losses	1	9
12 months or longer Fair Value	398	837
12 months or longer Unrealized Losses	6	6
Total Fair Value	1,161	4,887
Total Unrealized Losses	7	15
Held to maturity securities:
Less than 12 months Fair Value	7,638	6,795
Less than 12 months Unrealized Losses	34	35
12 months or longer Fair Value	556	376
12 months or longer Unrealized Losses	4	4
Total Fair Value	8,194	7,171
Total Unrealized Losses	38	39
Corporate debt securities [Member]
Available for sale securities:
Less than 12 months Fair Value	149	3,561
Less than 12 months Unrealized Losses	1	19
12 months or longer Fair Value	499	254
12 months or longer Unrealized Losses	0	1
Total Fair Value	648	3,815
Total Unrealized Losses	1	20
Held to maturity securities:
Less than 12 months Fair Value	416	2,909
Less than 12 months Unrealized Losses	1	29
12 months or longer Fair Value	354	1,066
12 months or longer Unrealized Losses	1	18
Total Fair Value	770	3,975
Total Unrealized Losses	$ 2	47
U.S. state and municipal securities [Member]
Held to maturity securities:
Less than 12 months Fair Value		77
Less than 12 months Unrealized Losses		2
12 months or longer Fair Value		18
12 months or longer Unrealized Losses		1
Total Fair Value		95
Total Unrealized Losses		3
Certificates of deposit [Member]
Available for sale securities:
Less than 12 months Fair Value		1,217
Less than 12 months Unrealized Losses		1
12 months or longer Fair Value		150
12 months or longer Unrealized Losses		0
Total Fair Value		1,367
Total Unrealized Losses		1
Non-agency commercial mortgage-backed securities [Member]
Held to maturity securities:
Less than 12 months Fair Value		283
Less than 12 months Unrealized Losses		2
12 months or longer Fair Value		632
12 months or longer Unrealized Losses		15
Total Fair Value		915
Total Unrealized Losses		17
U.S. agency notes [Member]
Available for sale securities:
Less than 12 months Fair Value		195
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		304
12 months or longer Unrealized Losses		2
Total Fair Value		499
Total Unrealized Losses		2
Foreign government agency securities [Member]
Available for sale securities:
Less than 12 months Fair Value		0
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		49
12 months or longer Unrealized Losses		1
Total Fair Value		49
Total Unrealized Losses		1
Held to maturity securities:
Less than 12 months Fair Value		0
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		49
12 months or longer Unrealized Losses		1
Total Fair Value		49
Total Unrealized Losses		$ 1