Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financial assets
Cash and due from banks	$ 24,874	$ 21,704
Deposits with banks	502,735	241,927
Federal funds sold and securities purchased under resale agreements	296,284	249,157
Investment securities, held-to-maturity	205,472	48,941
Loans, net of allowance for loan losses	44,474	44,955
Financial liabilities
Beneficial interests issued by consolidated VIEs	17,578	17,841
Carrying value
Financial assets
Cash and due from banks	24,900	21,700
Deposits with banks	502,700	241,900
Accrued interest and accounts receivable	89,400	71,300
Federal funds sold and securities purchased under resale agreements	58,300	234,600
Securities borrowed	107,700	133,500
Investment securities, held-to-maturity	201,800	47,500
Loans, net of allowance for loan losses	940,100	939,500
Other	81,800	61,300
Financial liabilities
Deposits	2,129,800	1,533,800
Federal funds purchased and securities loaned or sold under repurchase agreements	59,500	183,100
Short-term borrowings	28,300	35,000
Accounts payable and other liabilities	186,600	164,000
Beneficial interests issued by consolidated VIEs	17,500	17,800
Long-term debt	204,800	215,500
Wholesale lending-related commitments	2,200	1,200
Fair value
Financial assets
Cash and due from banks	24,900	21,700
Deposits with banks	502,700	241,900
Accrued interest and accounts receivable	89,400	71,300
Federal funds sold and securities purchased under resale agreements	58,300	234,600
Securities borrowed	107,700	133,500
Investment securities, held-to-maturity	205,500	48,900
Loans, net of allowance for loan losses	966,500	949,000
Other	81,900	61,400
Financial liabilities
Deposits	2,128,900	1,534,100
Federal funds purchased and securities loaned or sold under repurchase agreements	59,500	183,100
Short-term borrowings	28,300	35,000
Accounts payable and other liabilities	186,200	163,600
Beneficial interests issued by consolidated VIEs	17,600	17,900
Long-term debt	212,400	221,800
Wholesale lending-related commitments	2,100	1,900
Fair value | Level 1
Financial assets
Cash and due from banks	24,900	21,700
Deposits with banks	502,700	241,900
Accrued interest and accounts receivable	0	0
Federal funds sold and securities purchased under resale agreements	0	0
Securities borrowed	0	0
Investment securities, held-to-maturity	53,200	100
Loans, net of allowance for loan losses	0	0
Other	0	0
Financial liabilities
Deposits	0	0
Federal funds purchased and securities loaned or sold under repurchase agreements	0	0
Short-term borrowings	0	0
Accounts payable and other liabilities	0	100
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt	0	0
Wholesale lending-related commitments	0	0
Fair value | Level 2
Financial assets
Cash and due from banks	0	0
Deposits with banks	0	0
Accrued interest and accounts receivable	89,300	71,200
Federal funds sold and securities purchased under resale agreements	58,300	234,600
Securities borrowed	107,700	133,500
Investment securities, held-to-maturity	152,300	48,800
Loans, net of allowance for loan losses	210,900	214,100
Other	80,000	60,600
Financial liabilities
Deposits	2,128,900	1,534,100
Federal funds purchased and securities loaned or sold under repurchase agreements	59,500	183,100
Short-term borrowings	28,300	35,000
Accounts payable and other liabilities	181,900	160,000
Beneficial interests issued by consolidated VIEs	17,600	17,900
Long-term debt	209,200	218,300
Wholesale lending-related commitments	0	0
Fair value | Level 3
Financial assets
Cash and due from banks	0	0
Deposits with banks	0	0
Accrued interest and accounts receivable	100	100
Federal funds sold and securities purchased under resale agreements	0	0
Securities borrowed	0	0
Investment securities, held-to-maturity	0	0
Loans, net of allowance for loan losses	755,600	734,900
Other	1,900	800
Financial liabilities
Deposits	0	0
Federal funds purchased and securities loaned or sold under repurchase agreements	0	0
Short-term borrowings	0	0
Accounts payable and other liabilities	4,300	3,500
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt	3,200	3,500
Wholesale lending-related commitments	$ 2,100	$ 1,900