Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Financial Assets
Cash and due from banks	$ 65,832	$ 61,192
Investment securities held-to-maturity	69,311	74,088
Financial Liabilities
Long-term debt	52,720	51,480
Carrying Amount
Financial Assets
Cash and due from banks	65,832	61,192
Federal funds sold and securities purchased under resale agreements	4,408	2,543
Investment securities held-to-maturity	81,486	84,045
Loans held for sale	32	190
Loans	368,584	366,456
Other	2,084	2,377
Financial Liabilities
Time deposits	51,228	49,455
Short-term borrowings	14,215	12,976
Long-term debt	52,720	51,480
Other	4,860	5,432
Fair Value
Financial Assets
Cash and due from banks	65,832	61,192
Federal funds sold and securities purchased under resale agreements	4,408	2,543
Investment securities held-to-maturity	69,311	74,088
Loans held for sale	32	190
Loans	359,667	362,849
Other	2,084	2,377
Financial Liabilities
Time deposits	51,395	49,607
Short-term borrowings	13,983	12,729
Long-term debt	51,171	49,697
Other	4,860	5,432
Fair Value | Level 1
Financial Assets
Cash and due from banks	65,832	61,192
Federal funds sold and securities purchased under resale agreements	0	0
Investment securities held-to-maturity	1,256	1,310
Loans held for sale	0	0
Loans	0	0
Other	0	0
Financial Liabilities
Time deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Other	0	0
Fair Value | Level 2
Financial Assets
Cash and due from banks	0	0
Federal funds sold and securities purchased under resale agreements	4,408	2,543
Investment securities held-to-maturity	68,055	72,778
Loans held for sale	0	0
Loans	0	0
Other	1,556	1,863
Financial Liabilities
Time deposits	51,395	49,607
Short-term borrowings	13,983	12,729
Long-term debt	51,171	49,697
Other	1,359	1,406
Fair Value | Level 3
Financial Assets
Cash and due from banks	0	0
Federal funds sold and securities purchased under resale agreements	0	0
Investment securities held-to-maturity	0	0
Loans held for sale	32	190
Loans	359,667	362,849
Other	528	514
Financial Liabilities
Time deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Other	$ 3,501	$ 4,026