Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financial Assets:
Cash and due from banks	$ 3,145	$ 4,047
Interest-bearing deposits with banks	112,957	87,665
Securities purchased under resale agreements	6,679	6,692
Investment securities held-to-maturity	41,906	51,503
Financial Liabilities:
Non-interest-bearing	33,180	32,569
Interest-bearing - U.S.	166,483	121,738
Interest-bearing - non-U.S.	62,257	66,663
Securities sold under repurchase agreements	3,681	1,867
Other short-term borrowings	9,840	3,660
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans	14
Reported Amount
Financial Assets:
Cash and due from banks	3,145	4,047
Interest-bearing deposits with banks	112,957	87,665
Securities purchased under resale agreements	6,679	6,692
Investment securities held-to-maturity	47,727	57,117
Net loans	43,026	36,496
Other	6,752	6,866
Financial Liabilities:
Non-interest-bearing	33,180	32,569
Interest-bearing - U.S.	166,483	121,738
Interest-bearing - non-U.S.	62,257	66,663
Securities sold under repurchase agreements	3,681	1,867
Other short-term borrowings	9,840	3,660
Long-term debt	23,272	18,839
Other	6,752	6,866
Estimated Fair Value
Financial Assets:
Cash and due from banks	3,145	4,047
Interest-bearing deposits with banks	112,957	87,665
Securities purchased under resale agreements	6,679	6,692
Investment securities held-to-maturity	41,906	51,503
Net loans	42,839	36,335
Other	6,752	6,866
Financial Liabilities:
Non-interest-bearing	33,180	32,569
Interest-bearing - U.S.	166,483	121,738
Interest-bearing - non-U.S.	62,257	66,663
Securities sold under repurchase agreements	3,681	1,867
Other short-term borrowings	9,840	3,660
Long-term debt	23,078	18,417
Other	6,752	6,866
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	3,145	4,047
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	5,354	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	112,957	87,665
Securities purchased under resale agreements	6,679	6,692
Investment securities held-to-maturity	36,552	43,094
Net loans	41,097	34,308
Other	6,752	6,866
Financial Liabilities:
Non-interest-bearing	33,180	32,569
Interest-bearing - U.S.	166,483	121,738
Interest-bearing - non-U.S.	62,257	66,663
Securities sold under repurchase agreements	3,681	1,867
Other short-term borrowings	9,840	3,660
Long-term debt	22,882	18,216
Other	6,752	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	1,742	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	196	201
Other	$ 0	$ 0