Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financial Assets:
Cash and due from banks	$ 4,047	$ 3,970
Interest-bearing deposits with banks	87,665	101,593
Securities purchased under resale agreements	6,692	5,215
Investment securities held-to-maturity	51,503	57,913
Financial Liabilities:
Non-interest-bearing	32,569	46,755
Interest-bearing - U.S.	121,738	111,384
Interest-bearing - non-U.S.	66,663	77,325
Securities sold under repurchase agreements	1,867	1,177
Other short-term borrowings	2,660	2,097
Federal funds purchased	1,000	0
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans		5
Reported Amount
Financial Assets:
Cash and due from banks	4,047	3,970
Interest-bearing deposits with banks	87,665	101,593
Securities purchased under resale agreements	6,692	5,215
Investment securities held-to-maturity	57,117	64,700
Net loans	36,496	32,053
Other	6,866	3,626
Financial Liabilities:
Non-interest-bearing	32,569	46,755
Interest-bearing - U.S.	121,738	111,384
Interest-bearing - non-U.S.	66,663	77,325
Securities sold under repurchase agreements	1,867	1,177
Other short-term borrowings	2,660	2,097
Federal funds purchased	1,000
Long-term debt	18,839	14,996
Other	6,866	3,626
Estimated Fair Value
Financial Assets:
Cash and due from banks	4,047	3,970
Interest-bearing deposits with banks	87,665	101,593
Securities purchased under resale agreements	6,692	5,215
Investment securities held-to-maturity	51,503	57,913
Net loans	36,335	31,794
Other	6,866	3,626
Financial Liabilities:
Non-interest-bearing	32,569	46,755
Interest-bearing - U.S.	121,738	111,384
Interest-bearing - non-U.S.	66,663	77,325
Securities sold under repurchase agreements	1,867	1,177
Other short-term borrowings	2,660	2,097
Federal funds purchased	1,000
Long-term debt	18,417	14,273
Other	6,866	3,626
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,047	3,970
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	8,409	11,336
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
Federal funds purchased	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	87,665	101,593
Securities purchased under resale agreements	6,692	5,215
Investment securities held-to-maturity	43,094	46,577
Net loans	34,308	29,679
Other	6,866	3,626
Financial Liabilities:
Non-interest-bearing	32,569	46,755
Interest-bearing - U.S.	121,738	111,384
Interest-bearing - non-U.S.	66,663	77,325
Securities sold under repurchase agreements	1,867	1,177
Other short-term borrowings	2,660	2,097
Federal funds purchased	1,000
Long-term debt	18,216	14,102
Other	6,866	3,626
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	2,027	2,115
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
Federal funds purchased	0
Long-term debt	201	171
Other	$ 0	$ 0