Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Financial Assets
Cash and due from banks	$ 50,013	$ 56,502
Investment securities held-to-maturity	67,099	66,275
Financial Liabilities
Long-term debt	59,859	58,002
Carrying Amount
Financial Assets
Cash and due from banks	50,013	56,502
Federal funds sold and securities purchased under resale agreements	7,236	6,380
Investment securities held-to-maturity	78,008	78,634
Loans held for sale	42	322
Loans, net of allowance for losses	374,235	372,249
Other	2,584	2,482
Financial Liabilities
Time deposits	48,740	49,015
Short-term borrowings	14,765	13,583
Long-term debt	59,214	57,611
Other	4,565	5,220
Fair Value
Financial Assets
Cash and due from banks	50,013	56,502
Federal funds sold and securities purchased under resale agreements	7,236	6,380
Investment securities held-to-maturity	67,099	66,275
Loans held for sale	42	322
Loans, net of allowance for losses	369,966	365,628
Other	2,584	2,482
Financial Liabilities
Time deposits	48,823	49,156
Short-term borrowings	14,567	13,419
Long-term debt	58,346	56,441
Other	4,565	5,220
Fair Value | Level 1
Financial Assets
Cash and due from banks	50,013	56,502
Federal funds sold and securities purchased under resale agreements	0	0
Investment securities held-to-maturity	1,284	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	7,236	6,380
Investment securities held-to-maturity	65,815	65,000
Loans held for sale	0	0
Loans, net of allowance for losses	0	0
Other	1,930	1,767
Financial Liabilities
Time deposits	48,823	49,156
Short-term borrowings	14,567	13,419
Long-term debt	58,346	56,441
Other	1,350	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	42	322
Loans, net of allowance for losses	369,966	365,628
Other	654	715
Financial Liabilities
Time deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Other	$ 3,215	$ 3,851