Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Financial Assets:
Cash and due from banks	$ 4,433	$ 3,145
Interest-bearing deposits with banks	126,930	112,957
Securities purchased under resale agreements	6,812	6,679
Investment securities held-to-maturity	34,166	41,906
Other	854	767
Financial Liabilities:
Non-interest-bearing	35,267	33,180
Interest-bearing - U.S.	168,079	166,483
Interest-bearing - non-U.S.	71,004	62,257
Securities sold under repurchase agreements	841	3,681
Other short-term borrowings	3,821	9,840
Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Other	22	20
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans	92	14
Other	832	747
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Financial Assets:
Other	0	0
Carrying Value
Financial Assets:
Cash and due from banks	4,433	3,145
Interest-bearing deposits with banks	126,930	112,957
Securities purchased under resale agreements	6,812	6,679
Investment securities held-to-maturity	38,171	47,727
Net loans	46,589	43,026
Other	15,490	6,752
Financial Liabilities:
Non-interest-bearing	35,267	33,180
Interest-bearing - U.S.	168,079	166,483
Interest-bearing - non-U.S.	71,004	62,257
Securities sold under repurchase agreements	841	3,681
Other short-term borrowings	3,821	9,840
Long-term debt	25,143	23,272
Other	15,490	6,752
Estimated Fair Value
Financial Assets:
Cash and due from banks	4,433	3,145
Interest-bearing deposits with banks	126,930	112,957
Securities purchased under resale agreements	6,812	6,679
Investment securities held-to-maturity	34,166	41,906
Net loans	46,417	42,839
Other	15,490	6,752
Financial Liabilities:
Non-interest-bearing	35,267	33,180
Interest-bearing - U.S.	168,079	166,483
Interest-bearing - non-U.S.	71,004	62,257
Securities sold under repurchase agreements	841	3,681
Other short-term borrowings	3,821	9,840
Long-term debt	25,253	23,078
Other	15,490	6,752
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,433	3,145
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	563	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	126,930	112,957
Securities purchased under resale agreements	6,812	6,679
Investment securities held-to-maturity	33,603	36,552
Net loans	44,862	41,097
Other	15,490	6,752
Financial Liabilities:
Non-interest-bearing	35,267	33,180
Interest-bearing - U.S.	168,079	166,483
Interest-bearing - non-U.S.	71,004	62,257
Securities sold under repurchase agreements	841	3,681
Other short-term borrowings	3,821	9,840
Long-term debt	25,130	22,882
Other	15,490	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	1,555	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	123	196
Other	$ 0	$ 0