Fair Values of Assets and Liabilities - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Financial Assets
Cash and due from banks	$ 66,637	$ 56,502
Investment securities held-to-maturity	67,346	66,275
Financial Liabilities
Long-term debt	62,535	58,002
Carrying Amount
Financial Assets
Cash and due from banks	66,637	56,502
Federal funds sold and securities purchased under resale agreements	5,373	6,380
Investment securities held-to-maturity	76,931	78,634
Loans held for sale	202	322
Loans, net of allowance for losses	374,960	372,249
Other	2,281	2,482
Financial Liabilities
Time deposits	50,102	49,015
Short-term borrowings	12,857	13,583
Long-term debt	61,127	57,611
Other	4,628	5,220
Fair Value
Financial Assets
Cash and due from banks	66,637	56,502
Federal funds sold and securities purchased under resale agreements	5,373	6,380
Investment securities held-to-maturity	67,346	66,275
Loans held for sale	202	322
Loans, net of allowance for losses	373,152	365,628
Other	2,281	2,482
Financial Liabilities
Time deposits	50,149	49,156
Short-term borrowings	12,703	13,419
Long-term debt	60,837	56,441
Other	4,628	5,220
Fair Value | Level 1
Financial Assets
Cash and due from banks	66,637	56,502
Federal funds sold and securities purchased under resale agreements	0	0
Investment securities held-to-maturity	641	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	5,373	6,380
Investment securities held-to-maturity	66,705	65,000
Loans held for sale	0	0
Loans, net of allowance for losses	0	0
Other	1,637	1,767
Financial Liabilities
Time deposits	50,149	49,156
Short-term borrowings	12,703	13,419
Long-term debt	60,837	56,441
Other	1,399	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	202	322
Loans, net of allowance for losses	373,152	365,628
Other	644	715
Financial Liabilities
Time deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Other	$ 3,229	$ 3,851