Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financial Assets:
Cash and due from banks	$ 3,413	$ 4,047
Interest-bearing deposits with banks	125,486	87,665
Securities purchased under resale agreements	7,489	6,692
Investment securities held-to-maturity	46,823	51,503
Financial Liabilities:
Non-interest-bearing	37,367	32,569
Interest-bearing - U.S.	148,485	121,738
Interest-bearing - non-U.S.	66,032	66,663
Securities sold under repurchase agreements	3,576	1,867
Other short-term borrowings	11,541	3,660
Financing receivable, held-for-sale	17
Reported Amount
Financial Assets:
Cash and due from banks	3,413	4,047
Interest-bearing deposits with banks	125,486	87,665
Securities purchased under resale agreements	7,489	6,692
Investment securities held-to-maturity	52,914	57,117
Net loans	38,500	36,496
Other	6,866	6,866
Financial Liabilities:
Non-interest-bearing	37,367	32,569
Interest-bearing - U.S.	148,485	121,738
Interest-bearing - non-U.S.	66,032	66,663
Securities sold under repurchase agreements	3,576	1,867
Other short-term borrowings	11,541	3,660
Long-term debt	19,746	18,839
Other	6,866	6,866
Estimated Fair Value
Financial Assets:
Cash and due from banks	3,413	4,047
Interest-bearing deposits with banks	125,486	87,665
Securities purchased under resale agreements	7,489	6,692
Investment securities held-to-maturity	46,823	51,503
Net loans	38,266	36,335
Other	6,866	6,866
Financial Liabilities:
Non-interest-bearing	37,367	32,569
Interest-bearing - U.S.	148,485	121,738
Interest-bearing - non-U.S.	66,032	66,663
Securities sold under repurchase agreements	3,576	1,867
Other short-term borrowings	11,541	3,660
Long-term debt	19,361	18,417
Other	6,866	6,866
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	3,413	4,047
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	5,918	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	125,486	87,665
Securities purchased under resale agreements	7,489	6,692
Investment securities held-to-maturity	40,905	43,094
Net loans	36,300	34,308
Other	6,866	6,866
Financial Liabilities:
Non-interest-bearing	37,367	32,569
Interest-bearing - U.S.	148,485	121,738
Interest-bearing - non-U.S.	66,032	66,663
Securities sold under repurchase agreements	3,576	1,867
Other short-term borrowings	11,541	3,660
Long-term debt	19,156	18,216
Other	6,866	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	1,966	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	205	201
Other	$ 0	$ 0