Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financial Assets:
Cash and due from banks	$ 3,302	$ 3,212
Interest-bearing deposits with banks	68,965	73,040
Securities purchased under resale agreements	1,487	4,679
Investment securities held-to-maturity	42,157	41,351
Financial Liabilities:
Non-interest-bearing	34,031	44,804
Interest-bearing - U.S.	77,504	66,235
Interest-bearing - non-U.S.	70,337	69,321
Securities sold under repurchase agreements	1,102	1,082
Other short-term borrowings	839	3,092
Reported Amount
Financial Assets:
Cash and due from banks	3,302	3,212
Interest-bearing deposits with banks	68,965	73,040
Securities purchased under resale agreements	1,487	4,679
Investment securities held-to-maturity	41,782	41,914
Net loans (excluding leases)	26,235	25,722
Other	7,500	8,500
Financial Liabilities:
Non-interest-bearing	34,031	44,804
Interest-bearing - U.S.	77,504	66,235
Interest-bearing - non-U.S.	70,337	69,321
Securities sold under repurchase agreements	1,102	1,082
Other short-term borrowings	839	3,092
Long-term debt	12,509	11,093
Other	7,500	8,500
Estimated Fair Value
Financial Assets:
Cash and due from banks	3,302	3,212
Interest-bearing deposits with banks	68,965	73,040
Securities purchased under resale agreements	1,487	4,679
Investment securities held-to-maturity	42,157	41,351
Net loans (excluding leases)	26,292	25,561
Other	7,500	8,500
Financial Liabilities:
Non-interest-bearing	34,031	44,804
Interest-bearing - U.S.	77,504	66,235
Interest-bearing - non-U.S.	70,337	69,321
Securities sold under repurchase agreements	1,102	1,082
Other short-term borrowings	839	3,092
Long-term debt	12,770	11,048
Other	7,500	8,500
Estimated Fair Value | Nonrecurring Measurement Basis
Financial Assets:
Net loans (excluding leases)	9	10
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	3,302	3,212
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	10,299	14,541
Net loans (excluding leases)	0	0
Other	0	0
Financial Liabilities:
Non-interest-bearing	0	0
Interest-bearing - U.S.	0	0
Interest-bearing - non-U.S.	0	0
Securities sold under repurchase agreements	0	0
Other short-term borrowings	0	0
Long-term debt	0	0
Other	0	0
Estimated Fair Value | Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	68,965	73,040
Securities purchased under resale agreements	1,487	4,679
Investment securities held-to-maturity	31,682	26,688
Net loans (excluding leases)	24,432	24,648
Other	7,500	8,500
Financial Liabilities:
Non-interest-bearing	34,031	44,804
Interest-bearing - U.S.	77,504	66,235
Interest-bearing - non-U.S.	70,337	69,321
Securities sold under repurchase agreements	1,102	1,082
Other short-term borrowings	839	3,092
Long-term debt	12,621	10,865
Other	7,500	8,500
Estimated Fair Value | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	176	122
Net loans (excluding leases)	1,860	913
Other	0	0
Financial Liabilities:
Non-interest-bearing	0	0
Interest-bearing - U.S.	0	0
Interest-bearing - non-U.S.	0	0
Securities sold under repurchase agreements	0	0
Other short-term borrowings	0	0
Long-term debt	149	183
Other	$ 0	$ 0