Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financial assets
Cash and due from banks	$ 21,215	$ 22,324
Deposits with banks	235,382	256,469
Federal funds sold and securities purchased under resale agreements	257,391	321,588
Investment securities, held-to-maturity	42,377	31,458
Loans, net of allowance for loan losses	5,760	3,151
Financial liabilities
Beneficial interests issued by consolidated VIEs	18,515	20,241
Carrying value
Financial assets
Cash and due from banks	21,200	22,300
Deposits with banks	235,400	256,500
Accrued interest and accounts receivable	87,900	72,000
Federal funds sold and securities purchased under resale agreements	243,700	308,400
Securities borrowed	132,600	106,900
Investment securities, held-to-maturity	40,800	31,400
Loans, net of allowance for loan losses	926,200	968,000
Other	60,600	60,500
Financial liabilities
Deposits	1,495,900	1,447,400
Federal funds purchased and securities loaned or sold under repurchase agreements	246,800	181,400
Short-term borrowings	42,400	62,100
Accounts payable and other liabilities	181,500	160,600
Beneficial interests issued by consolidated VIEs	18,500	20,200
Long-term debt and junior subordinated deferrable interest debentures	224,300	227,100
Wholesale lending-related commitments	1,100	1,000
Total estimated fair value
Financial assets
Cash and due from banks	21,200	22,300
Deposits with banks	235,400	256,500
Accrued interest and accounts receivable	87,900	72,000
Federal funds sold and securities purchased under resale agreements	243,700	308,400
Securities borrowed	132,600	106,900
Investment securities, held-to-maturity	42,400	31,500
Loans, net of allowance for loan losses	939,600	970,000
Other	60,700	60,600
Financial liabilities
Deposits	1,496,300	1,447,500
Federal funds purchased and securities loaned or sold under repurchase agreements	246,800	181,400
Short-term borrowings	42,400	62,100
Accounts payable and other liabilities	181,100	160,200
Beneficial interests issued by consolidated VIEs	18,500	20,200
Long-term debt and junior subordinated deferrable interest debentures	226,900	227,900
Wholesale lending-related commitments	1,900	1,900
Total estimated fair value | Level 1
Financial assets
Cash and due from banks	21,200	22,300
Deposits with banks	235,400	256,500
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	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	700	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	87,900	71,900
Federal funds sold and securities purchased under resale agreements	243,700	308,400
Securities borrowed	132,600	106,900
Investment securities, held-to-maturity	42,400	31,500
Loans, net of allowance for loan losses	218,900	241,500
Other	59,800	59,600
Financial liabilities
Deposits	1,496,300	1,447,500
Federal funds purchased and securities loaned or sold under repurchase agreements	246,800	181,400
Short-term borrowings	42,400	62,100
Accounts payable and other liabilities	177,000	157,000
Beneficial interests issued by consolidated VIEs	18,500	20,200
Long-term debt and junior subordinated deferrable interest debentures	223,500	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	0	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	720,700	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	3,400	3,000
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt and junior subordinated deferrable interest debentures	3,400	3,300
Wholesale lending-related commitments	$ 1,900	$ 1,900