Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Available-for-sale securities, Amortized cost
Due in one year or less	$ 20,733
Due after one year through five years	146,823
Due after five years through 10 years	26,984
Due after 10 years	127,584
Amortized cost	322,124
Available-for-sale securities, Fair value
Due in one year or less	20,727
Due after one year through five years	142,437
Due after five years through 10 years	26,299
Due after 10 years	123,412
Fair value	$ 312,875	$ 308,525
Available-for-sale securities, Average yield
Due in one year or less	1.51%
Due after one year through five years	0.73%
Due after five years through 10 years	1.51%
Due after 10 years	2.56%
Average yield	1.57%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 29,440
Due after one year through five years	92,673
Due after five years through 10 years	92,973
Due after 10 years	151,538
Amortized cost	366,624
Total held-to-maturity securities, Fair value
Due in one year or less	29,255
Due after one year through five years	88,248
Due after five years through 10 years	87,247
Due after 10 years	145,744
Fair value	$ 350,494	362,628
Total held-to-maturity securities, Average yield
Due in one year or less	0.59%
Due after one year through five years	0.76%
Due after five years through 10 years	1.44%
Due after 10 years	2.54%
Average yield	1.66%
Supplemental information
US government agencies and US government sponsored enterprises residential MBS estimated duration	7 years
US government agencies and US government sponsored enterprises residential collateralized mortgage obligations estimated duration	4 years
U.S. nonagency residential collateralized mortgage obligations estimated duration	5 years
Minimum
Supplemental information
Due period of mortgage-backed securities and collateralized mortgage obligations	10 years
Mortgage-backed securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 5
Due after one year through five years	3,740
Due after five years through 10 years	4,314
Due after 10 years	96,768
Amortized cost	104,827
Available-for-sale securities, Fair value
Due in one year or less	5
Due after one year through five years	3,599
Due after five years through 10 years	4,467
Due after 10 years	92,249
Fair value	$ 100,320	83,562
Available-for-sale securities, Average yield
Due in one year or less	0.27%
Due after one year through five years	1.61%
Due after five years through 10 years	1.93%
Due after 10 years	2.49%
Average yield	2.43%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	1,435
Due after five years through 10 years	11,279
Due after 10 years	100,127
Amortized cost	112,841
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	1,379
Due after five years through 10 years	10,774
Due after 10 years	95,089
Fair value	$ 107,242	114,001
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	1.88%
Due after five years through 10 years	2.38%
Due after 10 years	2.82%
Average yield	2.77%
U.S. Treasury and government agencies
Available-for-sale securities, Amortized cost
Due in one year or less	$ 11,814
Due after one year through five years	136,391
Due after five years through 10 years	14,640
Due after 10 years	7,838
Amortized cost	170,683
Available-for-sale securities, Fair value
Due in one year or less	11,803
Due after one year through five years	132,200
Due after five years through 10 years	13,921
Due after 10 years	8,038
Fair value	$ 165,962	177,463
Available-for-sale securities, Average yield
Due in one year or less	0.83%
Due after one year through five years	0.59%
Due after five years through 10 years	1.20%
Due after 10 years	0.85%
Average yield	0.67%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 29,406
Due after one year through five years	91,162
Due after five years through 10 years	66,672
Due after 10 years	0
Amortized cost	187,240
Total held-to-maturity securities, Fair value
Due in one year or less	29,221
Due after one year through five years	86,797
Due after five years through 10 years	61,472
Due after 10 years	0
Fair value	$ 177,490	183,270
Total held-to-maturity securities, Average yield
Due in one year or less	0.58%
Due after one year through five years	0.74%
Due after five years through 10 years	1.26%
Due after 10 years	0.00%
Average yield	0.90%
Obligations of U.S. states and municipalities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 13
Due after one year through five years	144
Due after five years through 10 years	1,408
Due after 10 years	12,996
Amortized cost	14,561
Available-for-sale securities, Fair value
Due in one year or less	13
Due after one year through five years	145
Due after five years through 10 years	1,439
Due after 10 years	13,189
Fair value	$ 14,786	15,860
Available-for-sale securities, Average yield
Due in one year or less	4.09%
Due after one year through five years	4.58%
Due after five years through 10 years	4.84%
Due after 10 years	4.90%
Average yield	4.89%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 34
Due after one year through five years	76
Due after five years through 10 years	1,519
Due after 10 years	13,215
Amortized cost	14,844
Total held-to-maturity securities, Fair value
Due in one year or less	34
Due after one year through five years	72
Due after five years through 10 years	1,526
Due after 10 years	12,812
Fair value	$ 14,444	14,394
Total held-to-maturity securities, Average yield
Due in one year or less	3.75%
Due after one year through five years	2.78%
Due after five years through 10 years	3.79%
Due after 10 years	3.82%
Average yield	3.81%
Non-U.S. government debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 6,901
Due after one year through five years	5,305
Due after five years through 10 years	3,453
Due after 10 years	804
Amortized cost	16,463
Available-for-sale securities, Fair value
Due in one year or less	6,907
Due after one year through five years	5,276
Due after five years through 10 years	3,313
Due after 10 years	805
Fair value	$ 16,301	16,209
Available-for-sale securities, Average yield
Due in one year or less	2.67%
Due after one year through five years	2.58%
Due after five years through 10 years	1.12%
Due after 10 years	1.09%
Average yield	2.24%
Corporate debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	362
Due after five years through 10 years	14
Due after 10 years	0
Amortized cost	376
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	342
Due after five years through 10 years	14
Due after 10 years	0
Fair value	$ 356	$ 321
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	11.08%
Due after five years through 10 years	1.25%
Due after 10 years	0.00%
Average yield	10.71%
Asset-backed securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 2,000
Due after one year through five years	881
Due after five years through 10 years	3,155
Due after 10 years	9,178
Amortized cost	15,214
Available-for-sale securities, Fair value
Due in one year or less	1,999
Due after one year through five years	875
Due after five years through 10 years	3,145
Due after 10 years	9,131
Fair value	$ 15,150
Available-for-sale securities, Average yield
Due in one year or less	1.48%
Due after one year through five years	1.89%
Due after five years through 10 years	1.34%
Due after 10 years	1.59%
Average yield	1.54%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	0
Due after five years through 10 years	13,503
Due after 10 years	38,196
Amortized cost	51,699
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	0
Due after five years through 10 years	13,475
Due after 10 years	37,843
Fair value	$ 51,318
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	0.00%
Due after five years through 10 years	1.30%
Due after 10 years	1.37%
Average yield	1.35%