Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financial Assets:
Cash and due from banks	$ 4,009	$ 3,970
Interest-bearing deposits with banks	76,756	101,593
Securities purchased under resale agreements	1,816	5,215
Investment securities held-to-maturity	54,121	57,913
Financial Liabilities:
Non-interest-bearing	35,824	46,755
Interest-bearing - U.S.	118,561	111,384
Interest-bearing - non-U.S.	58,616	77,325
Securities sold under repurchase agreements	3,097	1,177
Short-term borrowings	8	2,097
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Liabilities:
Net loans (excluding leases)		5
Reported Amount
Financial Assets:
Cash and due from banks	4,009	3,970
Interest-bearing deposits with banks	76,756	101,593
Securities purchased under resale agreements	1,816	5,215
Investment securities held-to-maturity	61,956	64,700
Net loans	35,317	32,053
Other	6,869	3,626
Financial Liabilities:
Non-interest-bearing	35,824	46,755
Interest-bearing - U.S.	118,561	111,384
Interest-bearing - non-U.S.	58,616	77,325
Securities sold under repurchase agreements	3,097	1,177
Short-term borrowings	8	2,097
Long-term debt	18,564	14,996
Other	6,869	3,626
Estimated Fair Value
Financial Assets:
Cash and due from banks	4,009	3,970
Interest-bearing deposits with banks	76,756	101,593
Securities purchased under resale agreements	1,816	5,215
Investment securities held-to-maturity	54,121	57,913
Net loans	35,103	31,794
Other	6,869	3,626
Financial Liabilities:
Non-interest-bearing	35,824	46,755
Interest-bearing - U.S.	118,561	111,384
Interest-bearing - non-U.S.	58,616	77,325
Securities sold under repurchase agreements	3,097	1,177
Short-term borrowings	8	2,097
Long-term debt	17,661	14,273
Other	6,869	3,626
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,009	3,970
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	11,457	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
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	76,756	101,593
Securities purchased under resale agreements	1,816	5,215
Investment securities held-to-maturity	42,664	46,577
Net loans	33,055	29,679
Other	6,869	3,626
Financial Liabilities:
Non-interest-bearing	35,824	46,755
Interest-bearing - U.S.	118,561	111,384
Interest-bearing - non-U.S.	58,616	77,325
Securities sold under repurchase agreements	3,097	1,177
Short-term borrowings	8	2,097
Long-term debt	17,523	14,102
Other	6,869	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	2,048	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
Short-term borrowings	0	0
Long-term debt	138	171
Other	$ 0	$ 0