AFS Debt Securities, Contractual Maturities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 248,187	$ 260,060
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	14,359
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	7,131
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	22,374
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	204,323
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	251,229	263,459	[1]
Available-for-sale, fair value, remaining contractual maturity, due within one year	14,370
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	7,090
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	21,684
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 208,085
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	3.13%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	2.63%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	3.75%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	3.24%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	3.14%
Securities of U.S. Treasury and federal agencies [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 10,952
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	8,023
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	28
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	45
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	2,856
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	11,036	14,960
Available-for-sale, fair value, remaining contractual maturity, due within one year	8,029
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	29
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	49
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 2,929
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	2.10%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	2.32%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	1.97%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	1.84%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	1.49%
Securities of U.S. states and political subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 38,686
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	3,940
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	4,196
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	4,034
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	26,516
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	38,144	40,337
Available-for-sale, fair value, remaining contractual maturity, due within one year	3,963
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	4,244
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	4,039
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 25,898
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	3.15%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	4.58%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	3.20%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	2.78%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	2.98%
Mortgage-backed securities [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 159,107
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	2
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	155
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	2,138
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	156,812
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	164,644	167,214
Available-for-sale, fair value, remaining contractual maturity, due within one year	2
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	159
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	2,192
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 162,291
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	3.18%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	1.93%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	2.94%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	2.46%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	3.19%
Federal agencies [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 154,390
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	2
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	123
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	1,944
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	152,321
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	160,214	162,453
Available-for-sale, fair value, remaining contractual maturity, due within one year	2
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	128
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	2,005
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 158,079
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	3.19%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	1.93%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	3.06%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	2.44%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	3.20%
Residential [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 820
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	0
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	0
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	0
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	820
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	776	827
Available-for-sale, fair value, remaining contractual maturity, due within one year	0
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	0
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	0
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 776
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	3.19%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	0.00%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	0.00%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	0.00%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	3.19%
Commercial [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 3,897
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	0
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	32
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	194
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	3,671
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	3,654	3,934
Available-for-sale, fair value, remaining contractual maturity, due within one year	0
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	31
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	187
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 3,436
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	2.62%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	0.00%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	2.49%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	2.71%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	2.62%
Corporate debt securities [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 6,092
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	373
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	2,048
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	2,847
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	824
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	5,855	6,563
Available-for-sale, fair value, remaining contractual maturity, due within one year	355
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	1,973
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	2,755
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 772
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	4.97%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	4.12%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	5.18%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	5.03%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	4.67%
Collateralized loan and other debt obligations [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 26,873
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	0
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	0
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	12,014
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	14,859
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	25,168	29,695
Available-for-sale, fair value, remaining contractual maturity, due within one year	0
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	0
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	11,362
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 13,806
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	3.21%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	0.00%
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	0.00%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	3.29%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	3.15%
Other [Member]
Debt Securities, Available-for-sale, Amortized Cost, Fiscal Year Maturity [Abstract]
Available-for-sale, amortized cost, net	$ 6,477
Available-for-sale, amortized cost, net, remaining contractual maturity, due within one year	2,021
Available-for-sale, amortized cost, net, remaining contractual maturity, due after one year through five years	704
Available-for-sale, amortized cost, net, remaining contractual maturity, due after five years through ten years	1,296
Available-for-sale, amortized cost, net, remaining contractual maturity, due after ten years	2,456
Debt Securities, Available-for-sale, Fair Value, Fiscal Year Maturity [Abstract]
Available-for-sale, fair value	6,382	$ 4,690
Available-for-sale, fair value, remaining contractual maturity, due within one year	2,021
Available-for-sale, fair value, remaining contractual maturity, due after one year through five years	685
Available-for-sale, fair value, remaining contractual maturity, due after five years through ten years	1,287
Available-for-sale, fair value, remaining contractual maturity, due after ten years	$ 2,389
Debt Securities, Available-for-sale, Maturity, Weighted Average Yield [Abstract]
Available-for-sale, weighted average yield	1.51%
Available-for-sale, weighted average yield, remaining contractual maturity, due within one year	(0.22%)
Available-for-sale, weighted average yield, remaining contractual maturity, due after one year through five years	2.95%
Available-for-sale, weighted average yield, remaining contractual maturity, due after five years through ten years	1.41%
Available-for-sale, weighted average yield, remaining contractual maturity, due after ten years	2.57%

[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.