Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Available-for-sale securities, Amortized cost
Due in one year or less	$ 12,664
Due after one year through five years	139,816
Due after five years through 10 years	72,343
Due after 10 years	153,933
Amortized cost	378,756	$ 381,729
Available-for-sale securities, Fair value
Due in one year or less	12,704
Due after one year through five years	140,140
Due after five years through 10 years	71,661
Due after 10 years	155,437
Fair value	$ 379,942	388,178
Available-for-sale securities, Average yield
Due in one year or less	1.13%
Due after one year through five years	0.62%
Due after five years through 10 years	1.11%
Due after 10 years	2.57%
Average yield	1.52%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 1,318
Due after one year through five years	42,664
Due after five years through 10 years	56,296
Due after 10 years	117,268
Amortized cost	217,546
Total held-to-maturity securities, Fair value
Due in one year or less	1,319
Due after one year through five years	42,650
Due after five years through 10 years	55,195
Due after 10 years	118,546
Fair value	$ 217,710	205,472
Total held-to-maturity securities, Average yield
Due in one year or less	0.17%
Due after one year through five years	0.67%
Due after five years through 10 years	1.49%
Due after 10 years	2.84%
Average yield	2.05%
Supplemental information
US government agencies and US government sponsored enterprises residential MBS estimated duration	6 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	3 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	$ 0
Due after one year through five years	2,226
Due after five years through 10 years	5,998
Due after 10 years	117,531
Amortized cost	125,755	123,795
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	2,251
Due after five years through 10 years	6,283
Due after 10 years	117,555
Fair value	$ 126,089	126,390
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	1.40%
Due after five years through 10 years	1.79%
Due after 10 years	2.50%
Average yield	2.44%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	423
Due after five years through 10 years	11,858
Due after 10 years	92,851
Amortized cost	105,132
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	423
Due after five years through 10 years	12,214
Due after 10 years	93,816
Fair value	$ 106,453	117,830
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	1.12%
Due after five years through 10 years	2.36%
Due after 10 years	2.93%
Average yield	2.86%
U.S. Treasury and government agencies
Available-for-sale securities, Amortized cost
Due in one year or less	$ 4,058
Due after one year through five years	129,668
Due after five years through 10 years	53,799
Due after 10 years	7,898
Amortized cost	195,423	199,910
Available-for-sale securities, Fair value
Due in one year or less	4,088
Due after one year through five years	129,830
Due after five years through 10 years	52,724
Due after 10 years	8,142
Fair value	$ 194,784	201,951
Available-for-sale securities, Average yield
Due in one year or less	0.95%
Due after one year through five years	0.52%
Due after five years through 10 years	0.95%
Due after 10 years	0.54%
Average yield	0.65%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 1,318
Due after one year through five years	42,176
Due after five years through 10 years	32,613
Due after 10 years	0
Amortized cost	76,107
Total held-to-maturity securities, Fair value
Due in one year or less	1,319
Due after one year through five years	42,161
Due after five years through 10 years	31,065
Due after 10 years	0
Fair value	$ 74,545	53,234
Total held-to-maturity securities, Average yield
Due in one year or less	0.17%
Due after one year through five years	0.66%
Due after five years through 10 years	1.18%
Due after 10 years	0.00%
Average yield	0.88%
Obligations of U.S. states and municipalities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 33
Due after one year through five years	207
Due after five years through 10 years	1,152
Due after 10 years	17,259
Amortized cost	18,651	18,993
Available-for-sale securities, Fair value
Due in one year or less	33
Due after one year through five years	214
Due after five years through 10 years	1,219
Due after 10 years	18,456
Fair value	$ 19,922	20,396
Available-for-sale securities, Average yield
Due in one year or less	4.16%
Due after one year through five years	4.74%
Due after five years through 10 years	4.96%
Due after 10 years	4.96%
Average yield	4.96%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	65
Due after five years through 10 years	688
Due after 10 years	11,959
Amortized cost	12,712
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	66
Due after five years through 10 years	724
Due after 10 years	12,205
Fair value	$ 12,995	13,270
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	3.23%
Due after five years through 10 years	3.76%
Due after 10 years	3.77%
Average yield	3.77%
Non-U.S. government debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 7,029
Due after one year through five years	5,581
Due after five years through 10 years	4,511
Due after 10 years	3,624
Amortized cost	20,745	22,587
Available-for-sale securities, Fair value
Due in one year or less	7,038
Due after one year through five years	5,698
Due after five years through 10 years	4,530
Due after 10 years	3,607
Fair value	$ 20,873	22,928
Available-for-sale securities, Average yield
Due in one year or less	1.19%
Due after one year through five years	2.05%
Due after five years through 10 years	0.78%
Due after 10 years	0.52%
Average yield	1.21%
Corporate debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	139
Due after five years through 10 years	71
Due after 10 years	0
Amortized cost	210	215
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	136
Due after five years through 10 years	74
Due after 10 years	0
Fair value	$ 210	$ 216
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	1.18%
Due after five years through 10 years	1.89%
Due after 10 years	0.00%
Average yield	1.42%
Asset-backed securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 1,544
Due after one year through five years	1,995
Due after five years through 10 years	6,812
Due after 10 years	7,621
Amortized cost	17,972
Available-for-sale securities, Fair value
Due in one year or less	1,545
Due after one year through five years	2,011
Due after five years through 10 years	6,831
Due after 10 years	7,677
Fair value	$ 18,064
Available-for-sale securities, Average yield
Due in one year or less	1.28%
Due after one year through five years	1.94%
Due after five years through 10 years	1.30%
Due after 10 years	1.42%
Average yield	1.42%
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	11,137
Due after 10 years	12,458
Amortized cost	23,595
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	11,192
Due after 10 years	12,525
Fair value	$ 23,717
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	1.34%
Due after 10 years	1.33%
Average yield	1.33%