Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financial Assets:
Cash and due from banks	$ 4,552	$ 3,467
Interest-bearing deposits with banks	107,554	116,960
Securities purchased under resale agreements	5,238	3,106
Investment securities held-to-maturity	46,752	50,003
Financial Liabilities:
Non-interest-bearing	57,079	49,439
Interest-bearing - U.S.	108,372	102,331
Interest-bearing - non-U.S.	79,442	88,028
Securities sold under repurchase agreements	587	3,413
Other short-term borrowings	642	685
Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	200
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans (excluding leases)	7
Reported Amount
Financial Assets:
Cash and due from banks	4,552	3,467
Interest-bearing deposits with banks	107,554	116,960
Securities purchased under resale agreements	5,238	3,106
Investment securities held-to-maturity	46,261
Net loans (excluding leases)	31,467	27,803
Other	6,757	4,753
Financial Liabilities:
Non-interest-bearing	57,079
Interest-bearing - U.S.	108,372
Interest-bearing - non-U.S.	79,442
Securities sold under repurchase agreements	587
Other short-term borrowings	642
Long-term debt	13,836
Other	6,757	4,753
Reported Amount  | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	201	3,299
Estimated Fair Value
Financial Assets:
Cash and due from banks	4,552	3,467
Interest-bearing deposits with banks	107,554	116,960
Securities purchased under resale agreements	5,238	3,106
Investment securities held-to-maturity	46,953	50,003
Net loans (excluding leases)	31,512	27,884
Other	6,757	4,753
Financial Liabilities:
Non-interest-bearing	57,079	49,439
Interest-bearing - U.S.	108,372	102,331
Interest-bearing - non-U.S.	79,442	88,028
Securities sold under repurchase agreements	587	3,413
Other short-term borrowings	642	685
Long-term debt	13,904	14,162
Other	6,757	4,753
Estimated Fair Value | HTM securities purchased under the MMLF program
Financial Assets:
Investment securities held-to-maturity	201	3,304
Estimated Fair Value | Short-term borrowings under the MMLF program
Financial Liabilities:
Other short-term borrowings	200	3,302
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,552	3,467
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	5,566	6,115
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	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	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	107,554	116,960
Securities purchased under resale agreements	5,238	3,106
Investment securities held-to-maturity	41,337	43,888
Net loans (excluding leases)	29,340	25,668
Other	6,757	4,753
Financial Liabilities:
Non-interest-bearing	57,079	49,439
Interest-bearing - U.S.	108,372	102,331
Interest-bearing - non-U.S.	79,442	88,028
Securities sold under repurchase agreements	587	3,413
Other short-term borrowings	642	685
Long-term debt	13,801	14,049
Other	6,757	4,753
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	201	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	200	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	50	0
Net loans (excluding leases)	2,171	2,216
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	103	113
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	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	$ 0