Investment Securities - Amortized Cost and Estimated Fair Value by Contractual Maturity (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Available-for-sale securities, Amortized cost
Due in one year or less	$ 12,880
Due after one year through five years	104,944
Due after five years through 10 years	39,924
Due after 10 years	113,488
Amortized cost	271,236
Available-for-sale securities, Fair value
Due in one year or less	12,807
Due after one year through five years	104,841
Due after five years through 10 years	39,744
Due after 10 years	108,860
Fair value	$ 266,252	$ 201,704
Available-for-sale securities, Average yield
Due in one year or less	4.57%
Due after one year through five years	5.01%
Due after five years through 10 years	5.69%
Due after 10 years	5.15%
Average yield	5.15%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 32,167
Due after one year through five years	67,793
Due after five years through 10 years	74,375
Due after 10 years	149,536
Amortized cost	323,871
Total held-to-maturity securities, Fair value
Due in one year or less	31,852
Due after one year through five years	62,564
Due after five years through 10 years	65,366
Due after 10 years	135,021
Fair value	$ 294,803	342,754
Total held-to-maturity securities, Average yield
Due in one year or less	0.85%
Due after one year through five years	1.16%
Due after five years through 10 years	2.65%
Due after 10 years	3.86%
Average yield	2.72%
Supplemental information
Available for sale securities allowance for credit losses	$ 52
Unallocated portfolio layer fair value hedge basis adjustments	(1,300)
Held-to-maturity securities allowance for credit losses	$ 125
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	$ 3
Due after one year through five years	5,214
Due after five years through 10 years	4,659
Due after 10 years	74,903
Amortized cost	84,779
Available-for-sale securities, Fair value
Due in one year or less	3
Due after one year through five years	5,142
Due after five years through 10 years	4,654
Due after 10 years	71,098
Fair value	$ 80,897	91,612
Available-for-sale securities, Average yield
Due in one year or less	4.67%
Due after one year through five years	5.21%
Due after five years through 10 years	6.01%
Due after 10 years	4.82%
Average yield	4.91%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	7,374
Due after five years through 10 years	7,073
Due after 10 years	106,197
Amortized cost	120,644
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	6,803
Due after five years through 10 years	6,203
Due after 10 years	92,309
Fair value	$ 105,315	112,719
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	2.64%
Due after five years through 10 years	2.61%
Due after 10 years	3.00%
Average yield	2.96%
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	91,511
Due after five years through 10 years	29,421
Due after 10 years	6,958
Amortized cost	127,890
Available-for-sale securities, Fair value
Due in one year or less	0
Due after one year through five years	91,529
Due after five years through 10 years	29,504
Due after 10 years	6,495
Fair value	$ 127,528	57,805
Available-for-sale securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	5.03%
Due after five years through 10 years	6.01%
Due after 10 years	6.54%
Average yield	5.33%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 32,167
Due after one year through five years	60,115
Due after five years through 10 years	47,999
Due after 10 years	0
Amortized cost	140,281
Total held-to-maturity securities, Fair value
Due in one year or less	31,852
Due after one year through five years	55,456
Due after five years through 10 years	39,869
Due after 10 years	0
Fair value	$ 127,177	160,592
Total held-to-maturity securities, Average yield
Due in one year or less	0.85%
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	1.03%
Obligations of U.S. states and municipalities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 15
Due after one year through five years	17
Due after five years through 10 years	80
Due after 10 years	17,434
Amortized cost	17,546
Available-for-sale securities, Fair value
Due in one year or less	15
Due after one year through five years	17
Due after five years through 10 years	78
Due after 10 years	17,078
Fair value	$ 17,188	21,367
Available-for-sale securities, Average yield
Due in one year or less	2.25%
Due after one year through five years	3.48%
Due after five years through 10 years	4.26%
Due after 10 years	5.93%
Average yield	5.91%
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	271
Due after 10 years	9,256
Amortized cost	9,527
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	8,616
Fair value	$ 8,855	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	3.19%
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	$ 12,698
Due after one year through five years	7,643
Due after five years through 10 years	3,231
Due after 10 years	7,870
Amortized cost	31,442
Available-for-sale securities, Fair value
Due in one year or less	12,688
Due after one year through five years	7,595
Due after five years through 10 years	2,968
Due after 10 years	7,848
Fair value	$ 31,099	21,282
Available-for-sale securities, Average yield
Due in one year or less	4.50%
Due after one year through five years	4.66%
Due after five years through 10 years	1.78%
Due after 10 years	4.05%
Average yield	4.15%
Corporate debt securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 140
Due after one year through five years	0
Due after five years through 10 years	14
Due after 10 years	0
Amortized cost	154
Available-for-sale securities, Fair value
Due in one year or less	77
Due after one year through five years	0
Due after five years through 10 years	13
Due after 10 years	0
Fair value	$ 90	$ 100
Available-for-sale securities, Average yield
Due in one year or less	11.11%
Due after one year through five years	0.00%
Due after five years through 10 years	4.10%
Due after 10 years	0.00%
Average yield	10.48%
Asset-backed securities
Available-for-sale securities, Amortized cost
Due in one year or less	$ 24
Due after one year through five years	559
Due after five years through 10 years	2,519
Due after 10 years	6,323
Amortized cost	9,425
Available-for-sale securities, Fair value
Due in one year or less	24
Due after one year through five years	558
Due after five years through 10 years	2,527
Due after 10 years	6,341
Fair value	$ 9,450
Available-for-sale securities, Average yield
Due in one year or less	4.68%
Due after one year through five years	5.09%
Due after five years through 10 years	6.39%
Due after 10 years	6.87%
Average yield	6.63%
Total held-to-maturity securities, Amortized cost
Due in one year or less	$ 0
Due after one year through five years	304
Due after five years through 10 years	19,032
Due after 10 years	34,083
Amortized cost	53,419
Total held-to-maturity securities, Fair value
Due in one year or less	0
Due after one year through five years	305
Due after five years through 10 years	19,055
Due after 10 years	34,096
Fair value	$ 53,456
Total held-to-maturity securities, Average yield
Due in one year or less	0.00%
Due after one year through five years	6.76%
Due after five years through 10 years	6.19%
Due after 10 years	6.52%
Average yield	6.40%