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	Dec. 31, 2020	Dec. 31, 2019
Available for sale securities
Less than 12 months Fair Value	$ 63,104	$ 17,493
Less than 12 months Unrealized Losses	564	100
12 months or longer Fair Value	10,596	8,133
12 months or longer Unrealized Losses	83	40
Total Fair Value	73,700	25,626
Total Unrealized Losses	647	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
U.S. agency mortgage-backed securities [Member]
Available for sale securities
Less than 12 months Fair Value	61,706	16,023
Less than 12 months Unrealized Losses	551	94
12 months or longer Fair Value	4,774	6,592
12 months or longer Unrealized Losses	12	27
Total Fair Value	66,480	22,615
Total Unrealized Losses	563	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
Asset-backed securities [Member]
Available for sale securities
Less than 12 months Fair Value	1,398	960
Less than 12 months Unrealized Losses	13	6
12 months or longer Fair Value	5,822	298
12 months or longer Unrealized Losses	71	7
Total Fair Value	7,220	1,258
Total Unrealized Losses	$ 84	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. 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