Investment Securities (Available For Sale and Held to Maturity Securities with Unrealized Losses, Aggregated by Category and Period of Continuous Unrealized Loss) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Available for sale securities:
Less than 12 months Fair Value	$ 33,534	$ 17,493
Less than 12 months Unrealized Losses	743	100
12 months or longer Fair Value	14,311	8,133
12 months or longer Unrealized Losses	254	40
Total Fair Value	47,845	25,626
Total Unrealized Losses	997	140
Held to maturity securities:
Less than 12 months Fair Value		23,690
Less than 12 months Unrealized Losses		163
12 months or longer Fair Value		21,808
12 months or longer Unrealized Losses		202
Total Fair Value		45,498
Total Unrealized Losses		365
Total securities with unrealized losses
Less than 12 months Fair Value		41,183
Less than 12 months Unrealized Losses		263
12 months or longer Fair Value		29,941
12 months or longer Unrealized Losses		242
Total Fair Value		71,124
Total Unrealized Losses		505
Asset-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	15,852	960
Less than 12 months Unrealized Losses	515	6
12 months or longer Fair Value	2,638	298
12 months or longer Unrealized Losses	130	7
Total Fair Value	18,490	1,258
Total Unrealized Losses	645	13
Held to maturity securities:
Less than 12 months Fair Value		7,507
Less than 12 months Unrealized Losses		63
12 months or longer Fair Value		2,898
12 months or longer Unrealized Losses		22
Total Fair Value		10,405
Total Unrealized Losses		85
U.S. agency mortgage-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	11,077	16,023
Less than 12 months Unrealized Losses	100	94
12 months or longer Fair Value	11,661	6,592
12 months or longer Unrealized Losses	124	27
Total Fair Value	22,738	22,615
Total Unrealized Losses	224	121
Held to maturity securities:
Less than 12 months Fair Value		16,183
Less than 12 months Unrealized Losses		100
12 months or longer Fair Value		18,910
12 months or longer Unrealized Losses		180
Total Fair Value		35,093
Total Unrealized Losses		280
Corporate debt securities [Member]
Available for sale securities:
Less than 12 months Fair Value	4,835
Less than 12 months Unrealized Losses	106
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Total Fair Value	4,835
Total Unrealized Losses	106
Certificates of deposit [Member]
Available for sale securities:
Less than 12 months Fair Value	795
Less than 12 months Unrealized Losses	5
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Total Fair Value	795
Total Unrealized Losses	5
Non-agency commercial mortgage-backed securities [Member]
Available for sale securities:
Less than 12 months Fair Value	397
Less than 12 months Unrealized Losses	5
12 months or longer Fair Value	12
12 months or longer Unrealized Losses	0
Total Fair Value	409
Total Unrealized Losses	5
Commercial paper [Member]
Available for sale securities:
Less than 12 months Fair Value	396
Less than 12 months Unrealized Losses	1
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Total Fair Value	396
Total Unrealized Losses	1
U.S. state and municipal securities [Member]
Available for sale securities:
Less than 12 months Fair Value	182
Less than 12 months Unrealized Losses	11
12 months or longer Fair Value	0
12 months or longer Unrealized Losses	0
Total Fair Value	182
Total Unrealized Losses	$ 11
U.S. Treasury securities [Member]
Available for sale securities:
Less than 12 months Fair Value		510
Less than 12 months Unrealized Losses		0
12 months or longer Fair Value		1,243
12 months or longer Unrealized Losses		6
Total Fair Value		1,753
Total Unrealized Losses		$ 6