AFS and HTM Debt Securities HTM Debt Securities, Contractual Maturities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Held-to-maturity, amortized cost, net	$ 169,909	$ 153,933	[1]
Held-to-maturity, amortized cost, net, remaining contractual maturity, due within one year	8,347
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after one year through five years	37,182
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after five years through ten years	1,851
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after ten years	122,529
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity, fair value	177,562	156,860
Held-to-maturity, fair value, remaining contractual maturity, due after one year through five years	38,914
Held-to-maturity, fair value, remaining contractual maturity, due within one year	8,505
Held-to-maturity, fair value, remaining contractual maturity, due after five years through ten years	1,927
Held-to-maturity, fair value, remaining contractual maturity, due after ten years	$ 128,216
Debt Securities, Held-to-maturity, Maturity, Weighted Average Yield [Abstract]
Held-to-maturity weighted average yield	2.70%
Held-to-maturity, weighted average yield, remaining contractual maturity, due within one year	2.24%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after one year through five years	2.18%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after five years through ten years	2.78%
Held-to-maturity, weighed average yield, remaining contractual maturity, due after ten years	2.89%
US Treasury and Government [Member]
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Held-to-maturity, amortized cost, net	$ 48,569
Held-to-maturity, amortized cost, net, remaining contractual maturity, due within one year	8,336
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after one year through five years	36,454
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after five years through ten years	0
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after ten years	3,779
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity, fair value	50,691	46,139
Held-to-maturity, fair value, remaining contractual maturity, due after one year through five years	38,170
Held-to-maturity, fair value, remaining contractual maturity, due within one year	8,494
Held-to-maturity, fair value, remaining contractual maturity, due after five years through ten years	0
Held-to-maturity, fair value, remaining contractual maturity, due after ten years	$ 4,027
Debt Securities, Held-to-maturity, Maturity, Weighted Average Yield [Abstract]
Held-to-maturity weighted average yield	2.14%
Held-to-maturity, weighted average yield, remaining contractual maturity, due within one year	2.24%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after one year through five years	2.18%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after five years through ten years	0.00%
Held-to-maturity, weighed average yield, remaining contractual maturity, due after ten years	1.56%
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Held-to-maturity, amortized cost, net	$ 14,304
Held-to-maturity, amortized cost, net, remaining contractual maturity, due within one year	11
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after one year through five years	713
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after five years through ten years	1,724
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after ten years	11,856
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity, fair value	14,611	13,759
Held-to-maturity, fair value, remaining contractual maturity, due after one year through five years	731
Held-to-maturity, fair value, remaining contractual maturity, due within one year	11
Held-to-maturity, fair value, remaining contractual maturity, due after five years through ten years	1,794
Held-to-maturity, fair value, remaining contractual maturity, due after ten years	$ 12,075
Debt Securities, Held-to-maturity, Maturity, Weighted Average Yield [Abstract]
Held-to-maturity weighted average yield	2.71%
Held-to-maturity, weighted average yield, remaining contractual maturity, due within one year	1.95%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after one year through five years	2.22%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after five years through ten years	2.86%
Held-to-maturity, weighed average yield, remaining contractual maturity, due after ten years	2.72%
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Held-to-maturity, amortized cost, net	$ 107,013
Held-to-maturity, amortized cost, net, remaining contractual maturity, due within one year	0
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after one year through five years	15
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after five years through ten years	104
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after ten years	106,894
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity, fair value	112,238	96,925
Held-to-maturity, fair value, remaining contractual maturity, due after one year through five years	13
Held-to-maturity, fair value, remaining contractual maturity, due within one year	0
Held-to-maturity, fair value, remaining contractual maturity, due after five years through ten years	111
Held-to-maturity, fair value, remaining contractual maturity, due after ten years	$ 112,114
Debt Securities, Held-to-maturity, Maturity, Weighted Average Yield [Abstract]
Held-to-maturity weighted average yield	2.96%
Held-to-maturity, weighted average yield, remaining contractual maturity, due within one year	0.00%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after one year through five years	2.99%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after five years through ten years	1.37%
Held-to-maturity, weighed average yield, remaining contractual maturity, due after ten years	2.96%
Other debt securities [Member]
Debt Securities, Held-to-maturity, Maturity, Amortized Cost, Net [Abstract]
Held-to-maturity, amortized cost, net	$ 23
Held-to-maturity, amortized cost, net, remaining contractual maturity, due within one year	0
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after one year through five years	0
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after five years through ten years	23
Held-to-maturity, amortized cost, net, remaining contractual maturity, due after ten years	0
Debt Securities, Held-to-maturity, Maturity, Fair Value [Abstract]
Held-to-maturity, fair value	22	$ 37
Held-to-maturity, fair value, remaining contractual maturity, due after one year through five years	0
Held-to-maturity, fair value, remaining contractual maturity, due within one year	0
Held-to-maturity, fair value, remaining contractual maturity, due after five years through ten years	22
Held-to-maturity, fair value, remaining contractual maturity, due after ten years	$ 0
Debt Securities, Held-to-maturity, Maturity, Weighted Average Yield [Abstract]
Held-to-maturity weighted average yield	3.01%
Held-to-maturity, weighted average yield, remaining contractual maturity, due within one year	0.00%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after one year through five years	0.00%
Held-to-maturity, weighted average yield, remaining contractual maturity, due after five years through ten years	3.01%
Held-to-maturity, weighed average yield, remaining contractual maturity, due after ten years	0.00%

[1] (1) Prior to our adoption of CECL on January 1, 2020, the allowance for credit losses (ACL) related to available-for-sale (AFS) and held-to-maturity (HTM) debt securities was not applicable and is therefore presented as $0 at December 31, 2019. For more information, see Note 1 (Summary of Significant Accounting Policies) to Financial Statements in this Report.