Investment Securities - Amortized Cost, Fair Value and Yield by Maturity Date (Details) - USD ($) $ in Millions		3 Months Ended		12 Months Ended
		Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Amortized Cost
Amortized Cost		$ 82,948		$ 84,045
Fair Value
Fair Value		$ 71,149		$ 74,088
Weighted- Average Maturity in Years
Total		8 years 9 months 18 days
Weighted-Average Yield
Total		2.22%		2.22%
Weighted average maturity of total held to maturity investment securities				8 years 8 months 12 days
Amortized Cost
Amortized Cost		$ 79,407
Fair Value
Fair Value	[1]	$ 72,426		$ 69,706
Weighted- Average Maturity in Years
Total		6 years 6 months		6 years 3 months 18 days
Weighted-Average Yield
Total		3.33%		3.12%
Federal statutory rate		21.00%	21.00%
Portfolio basis adjustments excluded from amortized cost		$ 88
U.S. Treasury and agencies
Amortized Cost
Maturing in one year or less		50
Maturing after one year through five years		1,295
Maturing after five years through ten years		0
Maturing after ten years		0
Amortized Cost		1,345		$ 1,345
Fair Value
Maturing in one year or less		50
Maturing after one year through five years		1,253
Maturing after five years through ten years		0
Maturing after ten years		0
Fair Value		$ 1,303		1,310
Weighted- Average Maturity in Years
Maturing in one year or less		1 month 6 days
Maturing after one year through five years		2 years 1 month 6 days
Total		2 years
Weighted-Average Yield
Maturing in one year or less		2.67%
Maturing after one year through five years		2.85%
Maturing after five years through ten years		0.00%
Maturing after ten years		0.00%
Total		2.85%
Amortized Cost
Maturing in one year or less		$ 11
Maturing after one year through five years		13,391
Maturing after five years through ten years		8,608
Maturing after ten years		1,712
Amortized Cost		23,722
Fair Value
Maturing in one year or less		11
Maturing after one year through five years		12,738
Maturing after five years through ten years		7,445
Maturing after ten years		1,324
Fair Value		$ 21,518		19,542
Weighted- Average Maturity in Years
Maturing in one year or less		3 months 18 days
Maturing after one year through five years		3 years 8 months 12 days
Maturing after five years through ten years		7 years 1 month 6 days
Maturing after ten years		10 years 7 months 6 days
Total		5 years 6 months
Weighted-Average Yield
Maturing in one year or less		5.35%
Maturing after one year through five years		2.92%
Maturing after five years through ten years		2.20%
Maturing after ten years		2.02%
Total		2.60%
Mortgage-backed securities
Amortized Cost
Maturing in one year or less		$ 22
Maturing after one year through five years		1,286
Maturing after five years through ten years		74,832
Maturing after ten years		5,362
Amortized Cost		81,502
Fair Value
Maturing in one year or less		22
Maturing after one year through five years		1,273
Maturing after five years through ten years		64,221
Maturing after ten years		4,229
Fair Value		$ 69,745
Weighted- Average Maturity in Years
Maturing in one year or less		8 months 12 days
Maturing after one year through five years		2 years 7 months 6 days
Maturing after five years through ten years		8 years 10 months 24 days
Maturing after ten years		10 years 2 months 12 days
Total		8 years 10 months 24 days
Weighted-Average Yield
Maturing in one year or less		4.44%
Maturing after one year through five years		4.52%
Maturing after five years through ten years		2.19%
Maturing after ten years		1.92%
Total		2.21%
Amortized Cost
Maturing in one year or less		$ 95
Maturing after one year through five years		8,877
Maturing after five years through ten years		28,399
Maturing after ten years		1,130
Amortized Cost		38,501
Fair Value
Maturing in one year or less		92
Maturing after one year through five years		8,408
Maturing after five years through ten years		25,324
Maturing after ten years		953
Fair Value		$ 34,777
Weighted- Average Maturity in Years
Maturing in one year or less		9 months 18 days
Maturing after one year through five years		3 years 3 months 18 days
Maturing after five years through ten years		7 years 3 months 18 days
Maturing after ten years		10 years 10 months 24 days
Total		6 years 6 months
Weighted-Average Yield
Maturing in one year or less		2.16%
Maturing after one year through five years		3.25%
Maturing after five years through ten years		3.35%
Maturing after ten years		3.45%
Total		3.33%
Asset-backed securities
Amortized Cost
Maturing in one year or less		$ 10
Maturing after one year through five years		5,150
Maturing after five years through ten years		1,058
Maturing after ten years		0
Amortized Cost		6,218
Fair Value
Maturing in one year or less		10
Maturing after one year through five years		5,133
Maturing after five years through ten years		1,061
Maturing after ten years		0
Fair Value		$ 6,204		6,724
Weighted- Average Maturity in Years
Maturing in one year or less		10 months 24 days
Maturing after one year through five years		1 year 8 months 12 days
Maturing after five years through ten years		5 years 9 months 18 days
Total		2 years 4 months 24 days
Weighted-Average Yield
Maturing in one year or less		7.57%
Maturing after one year through five years		4.95%
Maturing after five years through ten years		7.05%
Maturing after ten years		0.00%
Total		5.31%
Obligations of state and political subdivisions
Amortized Cost
Maturing in one year or less		$ 137
Maturing after one year through five years		2,441
Maturing after five years through ten years		1,666
Maturing after ten years		6,582
Amortized Cost		10,826
Fair Value
Maturing in one year or less		138
Maturing after one year through five years		2,425
Maturing after five years through ten years		1,605
Maturing after ten years		5,619
Fair Value		$ 9,787		9,989
Weighted- Average Maturity in Years
Maturing in one year or less		3 months 18 days
Maturing after one year through five years		2 years 10 months 24 days
Maturing after five years through ten years		7 years 2 months 12 days
Maturing after ten years		15 years 6 months
Total		11 years 2 months 12 days
Weighted-Average Yield
Maturing in one year or less		5.91%
Maturing after one year through five years		4.65%
Maturing after five years through ten years		3.85%
Maturing after ten years		3.34%
Total		3.75%
Other
Amortized Cost
Maturing in one year or less		$ 16
Maturing after one year through five years		85
Maturing after five years through ten years		0
Maturing after ten years		0
Amortized Cost		101		8
Fair Value
Maturing in one year or less		16
Maturing after one year through five years		85
Maturing after five years through ten years		0
Maturing after ten years		0
Fair Value		$ 101		8
Weighted- Average Maturity in Years
Maturing in one year or less		1 year
Maturing after one year through five years		3 years 1 month 6 days
Total		2 years 9 months 18 days
Weighted-Average Yield
Maturing in one year or less		3.24%
Maturing after one year through five years		2.70%
Maturing after five years through ten years		0.00%
Maturing after ten years		0.00%
Total		2.79%
Amortized Cost
Maturing in one year or less		$ 0
Maturing after one year through five years		140
Maturing after five years through ten years		0
Maturing after ten years		0
Amortized Cost		140
Fair Value
Maturing in one year or less		0
Maturing after one year through five years		140
Maturing after five years through ten years		0
Maturing after ten years		0
Fair Value		$ 140		$ 24
Weighted- Average Maturity in Years
Maturing after one year through five years		2 years 4 months 24 days
Total		2 years 4 months 24 days
Weighted-Average Yield
Maturing in one year or less		0.00%
Maturing after one year through five years		4.92%
Maturing after five years through ten years		0.00%
Maturing after ten years		0.00%
Total		4.92%

[1] Includes only collateral pledged by the Company where counterparties have the right to sell or pledge the collateral.