Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Available-for-sale securities, Amortized cost
Due in one year or less	$ 5,114
Due after one year through five years	85,526
Due after five years through 10 years	41,806
Due after 10 years	108,629
Amortized cost	241,075
Available-for-sale securities, Fair value
Due in one year or less	5,034
Due after one year through five years	85,241
Due after five years through 10 years	41,759
Due after 10 years	104,118
Fair value	$ 236,152	$ 201,704
Available-for-sale securities, Average yield
Due in one year or less	3.50%
Due after one year through five years	4.99%
Due after five years through 10 years	5.79%
Due after 10 years	5.09%
Average yield	5.12%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 35,177
Due after one year through five years	66,607
Due after five years through 10 years	77,110
Due after 10 years	155,753
Amortized cost	334,647
Total held-to-maturity securities, Fair value
Due in one year or less	34,608
Due after one year through five years	61,235
Due after five years through 10 years	68,026
Due after 10 years	141,574
Fair value	$ 305,443	342,754
Total held-to-maturity securities, Average yield
Due in one year or less	0.88%
Due after one year through five years	1.11%
Due after five years through 10 years	2.73%
Due after 10 years	3.91%
Average yield	2.76%
Supplemental information
Available for sale securities allowance for credit losses	$ 34
Unallocated portfolio layer fair value hedge basis adjustments	(1,200)
Held-to-maturity securities allowance for credit losses	$ 120
US government agencies and US government sponsored enterprises residential MBS estimated duration	8 years
Agency residential collateralized mortgage obligations estimated duration	6 years
Nonagency residential collateralized mortgage obligations estimated duration	6 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	5,331
Due after five years through 10 years	4,742
Due after 10 years	70,816
Amortized cost	80,889
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	5,252
Due after five years through 10 years	4,773
Due after 10 years	66,832
Fair value	$ 76,857	91,612
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	5.32%
Due after five years through 10 years	6.20%
Due after 10 years	4.65%
Average yield	4.79%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	6,244
Due after five years through 10 years	8,239
Due after 10 years	108,871
Amortized cost	123,354
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	5,782
Due after five years through 10 years	7,275
Due after 10 years	95,418
Fair value	$ 108,475	112,719
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	2.57%
Due after five years through 10 years	2.65%
Due after 10 years	3.02%
Average yield	2.97%
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	74,048
Due after five years through 10 years	30,318
Due after 10 years	6,767
Amortized cost	111,133
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	73,880
Due after five years through 10 years	30,464
Due after 10 years	6,432
Fair value	$ 110,776	57,805
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	5.00%
Due after five years through 10 years	6.17%
Due after 10 years	6.70%
Average yield	5.42%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 35,177
Due after one year through five years	60,356
Due after five years through 10 years	48,191
Due after 10 years	0
Amortized cost	143,724
Total held-to-maturity securities, Fair value
Due in one year or less	34,608
Due after one year through five years	55,446
Due after five years through 10 years	40,118
Due after 10 years	0
Fair value	$ 130,172	160,592
Total held-to-maturity securities, Average yield
Due in one year or less	0.88%
Due after one year through five years	0.96%
Due after five years through 10 years	1.25%
Due after 10 years	0.00%
Average yield	1.04%
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	22
Due after five years through 10 years	115
Due after 10 years	18,931
Amortized cost	19,077
Available-for-sale securities, Fair value
Due in one year or less	8
Due after one year through five years	21
Due after five years through 10 years	114
Due after 10 years	18,668
Fair value	$ 18,811	21,367
Available-for-sale securities, Average yield
Due in one year or less	3.64%
Due after one year through five years	1.94%
Due after five years through 10 years	3.92%
Due after 10 years	5.95%
Average yield	5.93%
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	268
Due after 10 years	9,418
Amortized cost	9,686
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	239
Due after 10 years	8,774
Fair value	$ 9,013	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	3.15%
Due after 10 years	3.92%
Average yield	3.90%
Non-U.S. government debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 4,996
Due after one year through five years	5,337
Due after five years through 10 years	3,980
Due after 10 years	5,771
Amortized cost	20,084
Available-for-sale securities, Fair value
Due in one year or less	4,979
Due after one year through five years	5,304
Due after five years through 10 years	3,754
Due after 10 years	5,842
Fair value	$ 19,879	21,282
Available-for-sale securities, Average yield
Due in one year or less	3.31%
Due after one year through five years	4.56%
Due after five years through 10 years	2.10%
Due after 10 years	3.98%
Average yield	3.59%
Corporate debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 74
Due after one year through five years	64
Due after five years through 10 years	14
Due after 10 years	0
Amortized cost	152
Available-for-sale securities, Fair value
Due in one year or less	12
Due after one year through five years	64
Due after five years through 10 years	13
Due after 10 years	0
Fair value	$ 89	$ 100
Available-for-sale securities, Average yield
Due in one year or less	15.50%
Due after one year through five years	6.19%
Due after five years through 10 years	4.10%
Due after 10 years	0.00%
Average yield	10.51%
Asset-backed securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 35
Due after one year through five years	724
Due after five years through 10 years	2,637
Due after 10 years	6,344
Amortized cost	9,740
Available-for-sale securities, Fair value
Due in one year or less	35
Due after one year through five years	720
Due after five years through 10 years	2,641
Due after 10 years	6,344
Fair value	$ 9,740
Available-for-sale securities, Average yield
Due in one year or less	5.17%
Due after one year through five years	4.41%
Due after five years through 10 years	6.36%
Due after 10 years	6.80%
Average yield	6.50%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	7
Due after five years through 10 years	20,412
Due after 10 years	37,464
Amortized cost	57,883
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	7
Due after five years through 10 years	20,394
Due after 10 years	37,382
Fair value	$ 57,783
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	6.59%
Due after five years through 10 years	6.26%
Due after 10 years	6.52%
Average yield	6.43%