Fair Value - Schedule of Reported and Estimated Fair Values of Financial Assets and Liabilities Not Carried at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Financial Assets:
Cash and due from banks	$ 4,067	$ 4,047
Interest-bearing deposits with banks	105,121	87,665
Securities purchased under resale agreements	8,334	6,692
Investment securities held-to-maturity	44,925	51,503
Financial Liabilities:
Non-interest-bearing	31,448	32,569
Interest-bearing - U.S.	145,527	121,738
Interest-bearing - non-U.S.	70,454	66,663
Securities sold under repurchase agreements	2,119	1,867
Other short-term borrowings	10,018	3,660
Reported Amount
Financial Assets:
Cash and due from banks	4,067	4,047
Interest-bearing deposits with banks	105,121	87,665
Securities purchased under resale agreements	8,334	6,692
Investment securities held-to-maturity	49,477	57,117
Net loans	41,799	36,496
Other	6,744	6,866
Financial Liabilities:
Non-interest-bearing	31,448	32,569
Interest-bearing - U.S.	145,527	121,738
Interest-bearing - non-U.S.	70,454	66,663
Securities sold under repurchase agreements	2,119	1,867
Other short-term borrowings	10,018	3,660
Long-term debt	20,902	18,839
Other	6,744	6,866
Estimated Fair Value
Financial Assets:
Cash and due from banks	4,067	4,047
Interest-bearing deposits with banks	105,121	87,665
Securities purchased under resale agreements	8,334	6,692
Investment securities held-to-maturity	44,925	51,503
Net loans	41,632	36,335
Other	6,744	6,866
Financial Liabilities:
Non-interest-bearing	31,448	32,569
Interest-bearing - U.S.	145,527	121,738
Interest-bearing - non-U.S.	70,454	66,663
Securities sold under repurchase agreements	2,119	1,867
Other short-term borrowings	10,018	3,660
Long-term debt	20,895	18,417
Other	6,744	6,866
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,067	4,047
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	5,515	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	105,121	87,665
Securities purchased under resale agreements	8,334	6,692
Investment securities held-to-maturity	39,410	43,094
Net loans	39,849	34,308
Other	6,744	6,866
Financial Liabilities:
Non-interest-bearing	31,448	32,569
Interest-bearing - U.S.	145,527	121,738
Interest-bearing - non-U.S.	70,454	66,663
Securities sold under repurchase agreements	2,119	1,867
Other short-term borrowings	10,018	3,660
Long-term debt	20,671	18,216
Other	6,744	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	1,783	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	224	201
Other	$ 0	$ 0