Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financial Assets:
Cash and due from banks	$ 4,606	$ 3,467
Interest-bearing deposits with banks	107,553	116,960
Securities purchased under resale agreements	2,847	3,106
Investment securities held-to-maturity	43,728	50,003
Financial Liabilities:
Non-interest-bearing	64,885	49,439
Interest-bearing - U.S.	108,909	102,331
Interest-bearing - non-U.S.	85,579	88,028
Securities sold under repurchase agreements	637	3,413
Other short-term borrowings	549	685
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans (excluding leases)	61
Reported Amount
Financial Assets:
Cash and due from banks	4,606	3,467
Interest-bearing deposits with banks	107,553	116,960
Securities purchased under resale agreements	2,847	3,106
Investment securities held-to-maturity	43,346	48,929
Net loans (excluding leases)	32,702	27,803
Other		4,753
Financial Liabilities:
Non-interest-bearing	64,885	49,439
Interest-bearing - U.S.	108,909	102,331
Interest-bearing - non-U.S.	85,579	88,028
Securities sold under repurchase agreements	637	3,413
Other short-term borrowings	549	685
Long-term debt	12,978	13,805
Other		4,753
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	4,606	3,467
Interest-bearing deposits with banks	107,553	116,960
Securities purchased under resale agreements	2,847	3,106
Investment securities held-to-maturity	43,728	50,003
Net loans (excluding leases)	32,806	27,884
Other		4,753
Financial Liabilities:
Non-interest-bearing	64,885	49,439
Interest-bearing - U.S.	108,909	102,331
Interest-bearing - non-U.S.	85,579	88,028
Securities sold under repurchase agreements	637	3,413
Other short-term borrowings	549	685
Long-term debt	13,151	14,162
Other		4,753
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 | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,606	3,467
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	2,708	6,115
Net loans (excluding leases)	0	0
Other		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
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	107,553	116,960
Securities purchased under resale agreements	2,847	3,106
Investment securities held-to-maturity	41,020	43,888
Net loans (excluding leases)	30,292	25,668
Other		4,753
Financial Liabilities:
Non-interest-bearing	64,885	49,439
Interest-bearing - U.S.	108,909	102,331
Interest-bearing - non-U.S.	85,579	88,028
Securities sold under repurchase agreements	637	3,413
Other short-term borrowings	549	685
Long-term debt	13,069	14,049
Other		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		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	0
Net loans (excluding leases)	2,514	2,216
Other		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	$ 82	113
Other		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