Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Available-for-sale securities, Amortized cost
Due in one year or less	$ 19,870
Due after one year through five years	141,984
Due after five years through 10 years	53,298
Due after 10 years	119,457
Amortized cost	334,609
Available-for-sale securities, Fair value
Due in one year or less	19,817
Due after one year through five years	143,155
Due after five years through 10 years	53,357
Due after 10 years	118,219
Fair value	$ 334,548	$ 201,704
Available-for-sale securities, Average yield
Due in one year or less	4.69%
Due after one year through five years	4.86%
Due after five years through 10 years	5.12%
Due after 10 years	5.18%
Average yield	5.02%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 18,840
Due after one year through five years	64,146
Due after five years through 10 years	75,944
Due after 10 years	141,147
Amortized cost	300,077
Total held-to-maturity securities, Fair value
Due in one year or less	18,652
Due after one year through five years	60,829
Due after five years through 10 years	69,149
Due after 10 years	131,011
Fair value	$ 279,641	342,754
Total held-to-maturity securities, Average yield
Due in one year or less	0.84%
Due after one year through five years	1.19%
Due after five years through 10 years	2.69%
Due after 10 years	3.77%
Average yield	2.76%
Supplemental information
Available for sale securities allowance for credit losses	$ 52
Unallocated portfolio layer fair value hedge basis adjustments	694
Held-to-maturity securities allowance for credit losses	$ 123
US government agencies and US government sponsored enterprises residential MBS estimated duration	7 years
Agency residential collateralized mortgage obligations estimated duration	6 years
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	$ 3
Due after one year through five years	6,666
Due after five years through 10 years	4,501
Due after 10 years	79,616
Amortized cost	90,786
Available-for-sale securities, Fair value
Due in one year or less	3
Due after one year through five years	6,674
Due after five years through 10 years	4,557
Due after 10 years	78,295
Fair value	$ 89,529	91,612
Available-for-sale securities, Average yield
Due in one year or less	4.65%
Due after one year through five years	4.80%
Due after five years through 10 years	5.54%
Due after 10 years	4.91%
Average yield	4.94%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	7,383
Due after five years through 10 years	6,988
Due after 10 years	103,255
Amortized cost	117,626
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	7,034
Due after five years through 10 years	6,387
Due after 10 years	93,614
Fair value	$ 107,035	112,719
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	2.63%
Due after five years through 10 years	2.61%
Due after 10 years	2.99%
Average yield	2.94%
U.S. Treasury and government agencies
Available-for-sale securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	124,332
Due after five years through 10 years	39,682
Due after 10 years	6,975
Amortized cost	170,989
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	125,501
Due after five years through 10 years	39,785
Due after 10 years	6,896
Fair value	$ 172,182	57,805
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	4.90%
Due after five years through 10 years	5.40%
Due after 10 years	5.79%
Average yield	5.05%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 18,840
Due after one year through five years	56,638
Due after five years through 10 years	48,026
Due after 10 years	0
Amortized cost	123,504
Total held-to-maturity securities, Fair value
Due in one year or less	18,652
Due after one year through five years	53,670
Due after five years through 10 years	41,839
Due after 10 years	0
Fair value	$ 114,161	160,592
Total held-to-maturity securities, Average yield
Due in one year or less	0.84%
Due after one year through five years	0.99%
Due after five years through 10 years	1.25%
Due after 10 years	0.00%
Average yield	1.07%
Obligations of U.S. states and municipalities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 9
Due after one year through five years	14
Due after five years through 10 years	66
Due after 10 years	18,023
Amortized cost	18,112
Available-for-sale securities, Fair value
Due in one year or less	9
Due after one year through five years	13
Due after five years through 10 years	66
Due after 10 years	18,117
Fair value	$ 18,205	21,367
Available-for-sale securities, Average yield
Due in one year or less	1.47%
Due after one year through five years	3.19%
Due after five years through 10 years	4.25%
Due after 10 years	5.82%
Average yield	5.81%
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	304
Due after 10 years	9,145
Amortized cost	9,449
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	278
Due after 10 years	8,660
Fair value	$ 8,938	9,428
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	3.29%
Due after 10 years	3.94%
Average yield	3.92%
Non-U.S. government debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 19,745
Due after one year through five years	10,621
Due after five years through 10 years	6,796
Due after 10 years	5,465
Amortized cost	42,627
Available-for-sale securities, Fair value
Due in one year or less	19,753
Due after one year through five years	10,615
Due after five years through 10 years	6,685
Due after 10 years	5,500
Fair value	$ 42,553	21,282
Available-for-sale securities, Average yield
Due in one year or less	4.64%
Due after one year through five years	4.45%
Due after five years through 10 years	2.85%
Due after 10 years	3.86%
Average yield	4.21%
Corporate debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 108
Due after one year through five years	9
Due after five years through 10 years	5
Due after 10 years	0
Amortized cost	122
Available-for-sale securities, Fair value
Due in one year or less	47
Due after one year through five years	9
Due after five years through 10 years	5
Due after 10 years	0
Fair value	$ 61	$ 100
Available-for-sale securities, Average yield
Due in one year or less	13.80%
Due after one year through five years	4.06%
Due after five years through 10 years	4.19%
Due after 10 years	0.00%
Average yield	12.70%
Asset-backed securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 5
Due after one year through five years	342
Due after five years through 10 years	2,248
Due after 10 years	9,378
Amortized cost	11,973
Available-for-sale securities, Fair value
Due in one year or less	5
Due after one year through five years	343
Due after five years through 10 years	2,259
Due after 10 years	9,411
Fair value	$ 12,018
Available-for-sale securities, Average yield
Due in one year or less	6.16%
Due after one year through five years	5.91%
Due after five years through 10 years	6.36%
Due after 10 years	6.51%
Average yield	6.47%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	125
Due after five years through 10 years	20,626
Due after 10 years	28,747
Amortized cost	49,498
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	125
Due after five years through 10 years	20,645
Due after 10 years	28,737
Fair value	$ 49,507
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	6.52%
Due after five years through 10 years	6.05%
Due after 10 years	6.51%
Average yield	6.32%