Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financial assets
Cash and due from banks	$ 26,592	$ 24,874
Deposits with banks	678,829	502,735
Federal funds sold and securities purchased under resale agreements	260,987	296,284
Investment securities, held-to-maturity	342,853	205,472
Loans, net of allowance for loan losses	61,776	44,474
Financial liabilities
Beneficial interests issued by consolidated VIEs	14,403	17,578
Carrying value
Financial assets
Cash and due from banks	26,600	24,900
Deposits with banks	678,800	502,700
Accrued interest and accounts receivable	124,300	89,400
Federal funds sold and securities purchased under resale agreements	6,400	58,300
Securities borrowed	116,400	107,700
Investment securities, held-to-maturity	341,500	201,800
Loans, net of allowance for loan losses	959,700	940,100
Other	94,600	81,800
Financial liabilities
Deposits	2,291,200	2,129,800
Federal funds purchased and securities loaned or sold under repurchase agreements	69,600	59,500
Short-term borrowings	31,900	28,300
Accounts payable and other liabilities	214,500	186,600
Beneficial interests issued by consolidated VIEs	14,300	17,500
Long-term debt	224,100	204,800
Wholesale lending-related commitments	2,800	2,200
Total estimated fair value
Financial assets
Cash and due from banks	26,600	24,900
Deposits with banks	678,800	502,700
Accrued interest and accounts receivable	124,300	89,400
Federal funds sold and securities purchased under resale agreements	6,400	58,300
Securities borrowed	116,400	107,700
Investment securities, held-to-maturity	342,900	205,500
Loans, net of allowance for loan losses	981,700	966,500
Other	94,700	81,900
Financial liabilities
Deposits	2,291,200	2,128,900
Federal funds purchased and securities loaned or sold under repurchase agreements	69,600	59,500
Short-term borrowings	31,900	28,300
Accounts payable and other liabilities	214,200	186,200
Beneficial interests issued by consolidated VIEs	14,400	17,600
Long-term debt	231,400	212,400
Wholesale lending-related commitments	3,100	2,100
Total estimated fair value | Level 1
Financial assets
Cash and due from banks	26,600	24,900
Deposits with banks	678,800	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	181,900	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	124,200	89,300
Federal funds sold and securities purchased under resale agreements	6,400	58,300
Securities borrowed	116,400	107,700
Investment securities, held-to-maturity	161,000	152,300
Loans, net of allowance for loan losses	208,900	210,900
Other	93,100	80,000
Financial liabilities
Deposits	2,291,200	2,128,900
Federal funds purchased and securities loaned or sold under repurchase agreements	69,600	59,500
Short-term borrowings	31,900	28,300
Accounts payable and other liabilities	210,300	181,900
Beneficial interests issued by consolidated VIEs	14,400	17,600
Long-term debt	228,100	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	772,800	755,600
Other	1,600	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	3,900	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