Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financial assets
Cash and due from banks	$ 23,164	$ 22,324
Deposits with banks	244,874	256,469
Federal funds sold and securities purchased under resale agreements	267,864	321,588
Investment securities, held-to-maturity	32,072	31,458
Loans, net of allowance for loan losses	4,309	3,151
Financial liabilities
Beneficial interests issued by consolidated VIEs	25,585	20,241
Carrying value
Financial assets
Cash and due from banks	23,200	22,300
Deposits with banks	244,900	256,500
Accrued interest and accounts receivable	87,200	72,000
Federal funds sold and securities purchased under resale agreements	253,900	308,400
Securities borrowed	125,000	106,900
Investment securities, held-to-maturity	30,900	31,400
Loans, net of allowance for loan losses	939,400	968,000
Other	59,200	60,500
Financial liabilities
Deposits	1,491,400	1,447,400
Federal funds purchased and securities loaned or sold under repurchase agreements	200,700	181,400
Short-term borrowings	52,200	62,100
Accounts payable and other liabilities	175,800	160,600
Beneficial interests issued by consolidated VIEs	25,600	20,200
Long-term debt and junior subordinated deferrable interest debentures	220,800	227,100
Wholesale lending-related commitments	1,100	1,000
Total estimated fair value
Financial assets
Cash and due from banks	23,200	22,300
Deposits with banks	244,900	256,500
Accrued interest and accounts receivable	87,200	72,000
Federal funds sold and securities purchased under resale agreements	253,900	308,400
Securities borrowed	125,000	106,900
Investment securities, held-to-maturity	32,100	31,500
Loans, net of allowance for loan losses	951,900	970,000
Other	59,300	60,600
Financial liabilities
Deposits	1,491,800	1,447,500
Federal funds purchased and securities loaned or sold under repurchase agreements	200,700	181,400
Short-term borrowings	52,200	62,100
Accounts payable and other liabilities	175,400	160,200
Beneficial interests issued by consolidated VIEs	25,600	20,200
Long-term debt and junior subordinated deferrable interest debentures	224,900	227,900
Wholesale lending-related commitments	1,800	1,900
Total estimated fair value | Level 1
Financial assets
Cash and due from banks	23,200	22,300
Deposits with banks	244,900	256,500
Accrued interest and accounts receivable	800	0
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	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	100	200
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt and junior subordinated deferrable interest debentures	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	86,300	71,900
Federal funds sold and securities purchased under resale agreements	253,900	308,400
Securities borrowed	125,000	106,900
Investment securities, held-to-maturity	32,100	31,500
Loans, net of allowance for loan losses	224,100	241,500
Other	58,400	59,600
Financial liabilities
Deposits	1,491,800	1,447,500
Federal funds purchased and securities loaned or sold under repurchase agreements	200,700	181,400
Short-term borrowings	52,200	62,100
Accounts payable and other liabilities	172,200	157,000
Beneficial interests issued by consolidated VIEs	25,600	20,200
Long-term debt and junior subordinated deferrable interest debentures	221,600	224,600
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	727,800	728,500
Other	900	1,000
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	3,100	3,000
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt and junior subordinated deferrable interest debentures	3,300	3,300
Wholesale lending-related commitments	$ 1,800	$ 1,900