Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financial assets
Cash and due from banks	$ 25,857	$ 24,874
Deposits with banks	734,012	502,735
Federal funds sold and securities purchased under resale agreements	282,161	296,284
Investment securities, held-to-maturity	344,393	205,472
Loans, net of allowance for loan losses	60,628	44,474
Financial liabilities
Beneficial interests issued by consolidated VIEs	13,257	17,578
Carrying value
Financial assets
Cash and due from banks	25,900	24,900
Deposits with banks	734,000	502,700
Accrued interest and accounts receivable	115,700	89,400
Federal funds sold and securities purchased under resale agreements	9,000	58,300
Securities borrowed	130,200	107,700
Investment securities, held-to-maturity	343,500	201,800
Loans, net of allowance for loan losses	965,800	940,100
Other	98,000	81,800
Financial liabilities
Deposits	2,390,500	2,129,800
Federal funds purchased and securities loaned or sold under repurchase agreements	67,500	59,500
Short-term borrowings	30,400	28,300
Accounts payable and other liabilities	228,600	186,600
Beneficial interests issued by consolidated VIEs	13,200	17,500
Long-term debt	221,900	204,800
Wholesale lending-related commitments	2,100	2,200
Total estimated fair value
Financial assets
Cash and due from banks	25,900	24,900
Deposits with banks	734,000	502,700
Accrued interest and accounts receivable	115,700	89,400
Federal funds sold and securities purchased under resale agreements	9,000	58,300
Securities borrowed	130,200	107,700
Investment securities, held-to-maturity	344,400	205,500
Loans, net of allowance for loan losses	984,900	966,500
Other	98,100	81,900
Financial liabilities
Deposits	2,390,600	2,128,900
Federal funds purchased and securities loaned or sold under repurchase agreements	67,500	59,500
Short-term borrowings	30,400	28,300
Accounts payable and other liabilities	228,200	186,200
Beneficial interests issued by consolidated VIEs	13,200	17,600
Long-term debt	228,900	212,400
Wholesale lending-related commitments	3,100	2,100
Total estimated fair value | Level 1
Financial assets
Cash and due from banks	25,900	24,900
Deposits with banks	734,000	502,700
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	181,300	53,200
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	0
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt	0	0
Wholesale lending-related commitments	0	0
Total estimated fair value | Level 2
Financial assets
Cash and due from banks	0	0
Deposits with banks	0	0
Accrued interest and accounts receivable	115,600	89,300
Federal funds sold and securities purchased under resale agreements	9,000	58,300
Securities borrowed	130,200	107,700
Investment securities, held-to-maturity	163,100	152,300
Loans, net of allowance for loan losses	203,200	210,900
Other	96,700	80,000
Financial liabilities
Deposits	2,390,600	2,128,900
Federal funds purchased and securities loaned or sold under repurchase agreements	67,500	59,500
Short-term borrowings	30,400	28,300
Accounts payable and other liabilities	224,000	181,900
Beneficial interests issued by consolidated VIEs	13,200	17,600
Long-term debt	225,600	209,200
Wholesale lending-related commitments	0	0
Total estimated 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	781,700	755,600
Other	1,400	1,900
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	4,200	4,300
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt	3,300	3,200
Wholesale lending-related commitments	$ 3,100	$ 2,100