Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Financial Assets:
Cash and due from banks	$ 2,898	$ 4,047
Interest-bearing deposits with banks	99,876	87,665
Securities purchased under resale agreements	6,340	6,692
Investment securities held-to-maturity	44,916	51,503
Financial Liabilities:
Non-interest-bearing	34,519	32,569
Interest-bearing - U.S.	140,983	121,738
Interest-bearing - non-U.S.	63,658	66,663
Securities sold under repurchase agreements	2,716	1,867
Other short-term borrowings	13,571	3,660
Financing receivable, held-for-sale	8
Reported Amount
Financial Assets:
Cash and due from banks	2,898	4,047
Interest-bearing deposits with banks	99,876	87,665
Securities purchased under resale agreements	6,340	6,692
Investment securities held-to-maturity	51,051	57,117
Net loans	39,240	36,496
Other	6,746	6,866
Financial Liabilities:
Non-interest-bearing	34,519	32,569
Interest-bearing - U.S.	140,983	121,738
Interest-bearing - non-U.S.	63,658	66,663
Securities sold under repurchase agreements	2,716	1,867
Other short-term borrowings	13,571	3,660
Long-term debt	19,737	18,839
Other	6,746	6,866
Estimated Fair Value
Financial Assets:
Cash and due from banks	2,898	4,047
Interest-bearing deposits with banks	99,876	87,665
Securities purchased under resale agreements	6,340	6,692
Investment securities held-to-maturity	44,916	51,503
Net loans	39,053	36,335
Other	6,746	6,866
Financial Liabilities:
Non-interest-bearing	34,519	32,569
Interest-bearing - U.S.	140,983	121,738
Interest-bearing - non-U.S.	63,658	66,663
Securities sold under repurchase agreements	2,716	1,867
Other short-term borrowings	13,571	3,660
Long-term debt	19,569	18,417
Other	6,746	6,866
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	2,898	4,047
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	5,968	8,409
Net loans	0	0
Other	0	0
Financial Liabilities:
Non-interest-bearing	0	0
Interest-bearing - U.S.	0	0
Interest-bearing - non-U.S.	0	0
Securities sold under repurchase agreements	0	0
Other short-term borrowings	0	0
Long-term debt	0	0
Other	0	0
Estimated Fair Value | Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	99,876	87,665
Securities purchased under resale agreements	6,340	6,692
Investment securities held-to-maturity	38,948	43,094
Net loans	37,298	34,308
Other	6,746	6,866
Financial Liabilities:
Non-interest-bearing	34,519	32,569
Interest-bearing - U.S.	140,983	121,738
Interest-bearing - non-U.S.	63,658	66,663
Securities sold under repurchase agreements	2,716	1,867
Other short-term borrowings	13,571	3,660
Long-term debt	19,151	18,216
Other	6,746	6,866
Estimated Fair Value | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	0	0
Net loans	1,755	2,027
Other	0	0
Financial Liabilities:
Non-interest-bearing	0	0
Interest-bearing - U.S.	0	0
Interest-bearing - non-U.S.	0	0
Securities sold under repurchase agreements	0	0
Other short-term borrowings	0	0
Long-term debt	418	201
Other	$ 0	$ 0