Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Financial Assets
Cash and due from banks	$ 57,807	$ 56,502
Investment securities held-to-maturity	67,032	66,275
Financial Liabilities
Long-term debt	64,013	58,002
Carrying Amount
Financial Assets
Cash and due from banks	57,807	56,502
Federal funds sold and securities purchased under resale agreements	5,481	6,380
Investment securities held-to-maturity	77,879	78,634
Loans held for sale	3	322
Loans, net of allowance for losses	372,706	372,249
Other	2,585	2,482
Financial Liabilities
Time deposits	49,577	49,015
Short-term borrowings	12,615	13,583
Long-term debt	62,861	57,611
Other	4,723	5,220
Fair Value
Financial Assets
Cash and due from banks	57,807	56,502
Federal funds sold and securities purchased under resale agreements	5,481	6,380
Investment securities held-to-maturity	67,032	66,275
Loans held for sale	3	322
Loans, net of allowance for losses	368,767	365,628
Other	2,585	2,482
Financial Liabilities
Time deposits	49,604	49,156
Short-term borrowings	12,441	13,419
Long-term debt	62,111	56,441
Other	4,723	5,220
Fair Value | Level 1
Financial Assets
Cash and due from banks	57,807	56,502
Federal funds sold and securities purchased under resale agreements	0	0
Investment securities held-to-maturity	638	1,275
Loans held for sale	0	0
Loans, net of allowance for losses	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	5,481	6,380
Investment securities held-to-maturity	66,394	65,000
Loans held for sale	0	0
Loans, net of allowance for losses	0	0
Other	1,983	1,767
Financial Liabilities
Time deposits	49,604	49,156
Short-term borrowings	12,441	13,419
Long-term debt	62,111	56,441
Other	1,378	1,369
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	3	322
Loans, net of allowance for losses	368,767	365,628
Other	602	715
Financial Liabilities
Time deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Other	$ 3,345	$ 3,851