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, 2026	Dec. 31, 2025
Financial Assets:
Cash and due from banks	$ 6,518	$ 4,433
Interest-bearing deposits with banks	123,574	126,930
Securities purchased under resale agreements	8,187	6,812
Investment securities held-to-maturity	32,560	34,166
Other	893	854
Financial Liabilities:
Non-interest-bearing	39,643	35,267
Interest-bearing - U.S.	174,723	168,079
Interest-bearing - non-U.S.	78,975	71,004
Securities sold under repurchase agreements	969	841
Other short-term borrowings	3,981	3,821
Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Other	19	22
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans	74	92
Other	874	832
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Financial Assets:
Other	0	0
Carrying Value
Financial Assets:
Cash and due from banks	6,518	4,433
Interest-bearing deposits with banks	123,574	126,930
Securities purchased under resale agreements	8,187	6,812
Investment securities held-to-maturity	36,732	38,171
Net loans	49,022	46,589
Other	16,442	15,490
Financial Liabilities:
Non-interest-bearing	39,643	35,267
Interest-bearing - U.S.	174,723	168,079
Interest-bearing - non-U.S.	78,975	71,004
Securities sold under repurchase agreements	969	841
Other short-term borrowings	3,981	3,821
Long-term debt	25,233	25,143
Other	16,442	15,490
Estimated Fair Value
Financial Assets:
Cash and due from banks	6,518	4,433
Interest-bearing deposits with banks	123,574	126,930
Securities purchased under resale agreements	8,187	6,812
Investment securities held-to-maturity	32,560	34,166
Net loans	48,867	46,417
Other	16,442	15,490
Financial Liabilities:
Non-interest-bearing	39,643	35,267
Interest-bearing - U.S.	174,723	168,079
Interest-bearing - non-U.S.	78,975	71,004
Securities sold under repurchase agreements	969	841
Other short-term borrowings	3,981	3,821
Long-term debt	25,008	25,253
Other	16,442	15,490
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	6,518	4,433
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	265	563
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	123,574	126,930
Securities purchased under resale agreements	8,187	6,812
Investment securities held-to-maturity	32,295	33,603
Net loans	47,587	44,862
Other	16,442	15,490
Financial Liabilities:
Non-interest-bearing	39,643	35,267
Interest-bearing - U.S.	174,723	168,079
Interest-bearing - non-U.S.	78,975	71,004
Securities sold under repurchase agreements	969	841
Other short-term borrowings	3,981	3,821
Long-term debt	24,857	25,130
Other	16,442	15,490
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	1,281	1,555
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	151	123
Other	$ 0	$ 0