Fair Value, Assets and Liabilities, Fair Value Estimates for Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021	Mar. 31, 2021
Financial assets
Cash and due from banks	$ 27,454	$ 24,616
Interest-earning deposits with banks	174,441	209,614
Federal funds sold and securities purchased under resale agreements	67,764	66,223
Held-to-maturity debt securities	280,808	272,022
Loans held for sale	19,824	23,617
Loans, net	900,303	882,904
Financial liabilities
Deposits	1,481,354	1,482,479	$ 1,437,119
Short-term borrowings	33,601	34,409
Long-term debt	153,337	160,689
Carrying value [Member]
Financial assets
Cash and due from banks	27,454	24,616
Interest-earning deposits with banks	174,441	209,614
Federal funds sold and securities purchased under resale agreements	67,764	66,223
Held-to-maturity debt securities	280,808	272,022
Loans held for sale	6,669	7,722
Loans, net	885,950	868,278
Nonmarketable equity securities	3,584	3,584
Total financial assets	1,446,670	1,452,059
Financial liabilities
Deposits	26,648	30,012
Short-term borrowings	33,433	34,409
Long-term debt	153,243	160,660
Total financial liabilities	213,324	225,081
Fair Value Disclosures, Textual [Abstract]
Deposit liabilities with no defined or contractual maturity	1,500,000	1,500,000
Carrying value [Member] | Finance leases [Member]
Financial liabilities
Long-term debt	25	26
Carrying value [Member] | Commercial lease financing [Member]
Financial assets
Loans, net	14,200	14,500
Estimated fair value [Member]
Financial assets
Cash and due from banks	27,454	24,616
Interest-earning deposits with banks	174,441	209,614
Federal funds sold and securities purchased under resale agreements	67,764	66,223
Held-to-maturity debt securities	264,641	272,386
Loans held for sale	6,753	7,929
Loans, net	878,605	883,963
Nonmarketable equity securities	3,648	3,646
Total financial assets	1,423,306	1,468,377
Financial liabilities
Deposits	26,201	30,002
Short-term borrowings	33,433	34,409
Long-term debt	157,458	168,084
Total financial liabilities	217,092	232,495
Fair Value Disclosures, Textual [Abstract]
Loan commitments and standby, commercial and similar letters of credit	1,300	1,400
Estimated fair value [Member] | Fair Value, Inputs, Level 1 [Member]
Financial assets
Cash and due from banks	27,454	24,616
Interest-earning deposits with banks	174,296	209,452
Federal funds sold and securities purchased under resale agreements	0	0
Held-to-maturity debt securities	15,551	16,825
Loans held for sale	0	0
Loans, net	0	0
Nonmarketable equity securities	0	0
Total financial assets	217,301	250,893
Financial liabilities
Deposits	0	0
Short-term borrowings	0	0
Long-term debt	0	0
Total financial liabilities	0	0
Estimated fair value [Member] | Fair value, inputs, level 2 [Member]
Financial assets
Cash and due from banks	0	0
Interest-earning deposits with banks	145	162
Federal funds sold and securities purchased under resale agreements	67,764	66,223
Held-to-maturity debt securities	246,325	252,717
Loans held for sale	5,097	6,300
Loans, net	62,483	63,404
Nonmarketable equity securities	0	0
Total financial assets	381,814	388,806
Financial liabilities
Deposits	11,542	14,401
Short-term borrowings	33,433	34,409
Long-term debt	156,237	166,682
Total financial liabilities	201,212	215,492
Estimated fair value [Member] | Fair value, inputs, level 3 [Member]
Financial assets
Cash and due from banks	0	0
Interest-earning deposits with banks	0	0
Federal funds sold and securities purchased under resale agreements	0	0
Held-to-maturity debt securities	2,765	2,844
Loans held for sale	1,656	1,629
Loans, net	816,122	820,559
Nonmarketable equity securities	3,648	3,646
Total financial assets	824,191	828,678
Financial liabilities
Deposits	14,659	15,601
Short-term borrowings	0	0
Long-term debt	1,221	1,402
Total financial liabilities	$ 15,880	$ 17,003