Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financial Assets:
Cash and due from banks	$ 4,619	$ 3,467
Interest-bearing deposits with banks	113,347	116,960
Securities purchased under resale agreements	3,997	3,106
Investment securities held-to-maturity	45,685	50,003
Financial Liabilities:
Non-interest-bearing	61,742	49,439
Interest-bearing - U.S.	111,291	102,331
Interest-bearing - non-U.S.	90,936	88,028
Securities sold under repurchase agreements	658	3,413
Other short-term borrowings	635	685
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Net loans (excluding leases)	19
Reported Amount
Financial Assets:
Cash and due from banks	4,619	3,467
Interest-bearing deposits with banks	113,347	116,960
Securities purchased under resale agreements	3,997	3,106
Investment securities held-to-maturity	45,182	48,929
Net loans (excluding leases)	30,604	27,803
Other		4,753
Financial Liabilities:
Non-interest-bearing	61,742	49,439
Interest-bearing - U.S.	111,291	102,331
Interest-bearing - non-U.S.	90,936	88,028
Securities sold under repurchase agreements	658	3,413
Other short-term borrowings	635	685
Long-term debt	13,032	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	4,619	3,467
Interest-bearing deposits with banks	113,347	116,960
Securities purchased under resale agreements	3,997	3,106
Investment securities held-to-maturity	45,685	50,003
Net loans (excluding leases)	30,661	27,884
Other		4,753
Financial Liabilities:
Non-interest-bearing	61,742	49,439
Interest-bearing - U.S.	111,291	102,331
Interest-bearing - non-U.S.	90,936	88,028
Securities sold under repurchase agreements	658	3,413
Other short-term borrowings	635	685
Long-term debt	13,228	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	4,619	3,467
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held-to-maturity	4,711	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	113,347	116,960
Securities purchased under resale agreements	3,997	3,106
Investment securities held-to-maturity	40,974	43,888
Net loans (excluding leases)	28,242	25,668
Other		4,753
Financial Liabilities:
Non-interest-bearing	61,742	49,439
Interest-bearing - U.S.	111,291	102,331
Interest-bearing - non-U.S.	90,936	88,028
Securities sold under repurchase agreements	658	3,413
Other short-term borrowings	635	685
Long-term debt	13,136	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)	2,419	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	$ 92	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