Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financial Assets:
Cash and due from banks	$ 3,467	$ 3,302
Interest-bearing deposits with banks	116,960	68,965
Securities purchased under resale agreements	3,106	1,487
Investment securities held-to-maturity	50,003	42,157
Financial Liabilities:
Non-interest-bearing	49,439	34,031
Interest-bearing - U.S.	102,331	77,504
Interest-bearing - non-U.S.	88,028	70,337
Securities sold under repurchase agreements	3,413	1,102
Other short-term borrowings	685	839
Reported Amount
Financial Assets:
Cash and due from banks	3,467	3,302
Interest-bearing deposits with banks	116,960	68,965
Securities purchased under resale agreements	3,106	1,487
Investment securities held-to-maturity	48,929	41,782
Net loans (excluding leases)	27,803	26,325
Other	4,753	7,500
Financial Liabilities:
Non-interest-bearing	49,439	34,031
Interest-bearing - U.S.	102,331	77,504
Interest-bearing - non-U.S.	88,028	70,337
Securities sold under repurchase agreements	3,413	1,102
Other short-term borrowings	685	839
Long-term debt	13,805	12,509
Other	4,753	7,500
Reported Amount  | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	3,299
Reported Amount  | Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	3,302
Estimated Fair Value
Financial Assets:
Cash and due from banks	3,467	3,302
Interest-bearing deposits with banks	116,960	68,965
Securities purchased under resale agreements	3,106	1,487
Investment securities held-to-maturity	50,003	42,157
Net loans (excluding leases)	27,884	26,292
Other	4,753	7,500
Financial Liabilities:
Non-interest-bearing	49,439	34,031
Interest-bearing - U.S.	102,331	77,504
Interest-bearing - non-U.S.	88,028	70,337
Securities sold under repurchase agreements	3,413	1,102
Other short-term borrowings	685	839
Long-term debt	14,162	12,770
Other	4,753	7,500
Estimated Fair Value | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	3,304
Estimated Fair Value | Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	3,302
Estimated Fair Value | Nonrecurring Measurement Basis
Financial Assets:
Net loans (excluding leases)		9
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	3,467	3,302
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	6,115	10,299
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 | Quoted Market Prices in Active Markets (Level 1) | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	0
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1) | Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	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	116,960	68,965
Securities purchased under resale agreements	3,106	1,487
Investment securities held-to-maturity	43,888	31,682
Net loans (excluding leases)	25,668	24,432
Other	4,753	7,500
Financial Liabilities:
Non-interest-bearing	49,439	34,031
Interest-bearing - U.S.	102,331	77,504
Interest-bearing - non-U.S.	88,028	70,337
Securities sold under repurchase agreements	3,413	1,102
Other short-term borrowings	685	839
Long-term debt	14,049	12,621
Other	4,753	7,500
Estimated Fair Value | Pricing Methods with Significant Observable Market Inputs (Level 2)  | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	3,304
Estimated Fair Value | Pricing Methods with Significant Observable Market Inputs (Level 2)  | Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	3,302
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	0	176
Net loans (excluding leases)	2,216	1,860
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	113	149
Other	0	$ 0
Estimated Fair Value | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	0
Estimated Fair Value | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	$ 0