Fair Value - Schedule of Reported and Estimated Fair Values of Financial Assets and Liabilities Not Carried at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Financial Assets:
Cash and due from banks	$ 4,658	$ 3,145
Interest-bearing deposits with banks	119,464	112,957
Securities purchased under resale agreements	7,971	6,679
Investment securities held-to-maturity	40,424	41,906
Financial Liabilities:
Non-interest-bearing	32,265	33,180
Interest-bearing - U.S.	168,362	166,483
Interest-bearing - non-U.S.	71,429	62,257
Securities sold under repurchase agreements	3,524	3,681
Other short-term borrowings	11,849	9,840
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans	20	14
Reported Amount
Financial Assets:
Cash and due from banks	4,658
Interest-bearing deposits with banks	119,464
Securities purchased under resale agreements	7,971
Investment securities held-to-maturity	45,505	47,727
Net loans		43,026
Other	9,742	6,752
Financial Liabilities:
Non-interest-bearing		33,180
Interest-bearing - U.S.		166,483
Interest-bearing - non-U.S.		62,257
Securities sold under repurchase agreements		3,681
Other short-term borrowings		9,840
Long-term debt	24,846	23,272
Other	9,742	6,752
Estimated Fair Value
Financial Assets:
Cash and due from banks	4,658	3,145
Interest-bearing deposits with banks	119,464	112,957
Securities purchased under resale agreements	7,971	6,679
Investment securities held-to-maturity	40,424	41,906
Net loans	44,315	42,839
Other	9,742	6,752
Financial Liabilities:
Non-interest-bearing	32,265	33,180
Interest-bearing - U.S.	168,362	166,483
Interest-bearing - non-U.S.	71,429	62,257
Securities sold under repurchase agreements	3,524	3,681
Other short-term borrowings	11,849	9,840
Long-term debt	24,614	23,078
Other	9,742	6,752
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,658	3,145
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	4,376	5,354
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	119,464	112,957
Securities purchased under resale agreements	7,971	6,679
Investment securities held-to-maturity	36,048	36,552
Net loans	42,564	41,097
Other	9,742	6,752
Financial Liabilities:
Non-interest-bearing	32,265	33,180
Interest-bearing - U.S.	168,362	166,483
Interest-bearing - non-U.S.	71,429	62,257
Securities sold under repurchase agreements	3,524	3,681
Other short-term borrowings	11,849	9,840
Long-term debt	24,510	22,882
Other	9,742	6,752
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	1,751	1,742
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	104	196
Other	$ 0	$ 0