Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financial assets
Cash and due from banks	$ 22,324	$ 25,898
Deposits with banks	256,469	405,406
Federal funds sold and securities purchased under resale agreements	321,588	198,422
Investment securities, held-to-maturity	31,458	48,652
Loans, net of allowance for loan losses	3,151	2,508
Financial liabilities
Beneficial interests issued by consolidated VIEs	20,241	26,081
Carrying value
Financial assets
Cash and due from banks	22,300	25,900
Deposits with banks	256,500	405,400
Accrued interest and accounts receivable	72,000	67,000
Federal funds sold and securities purchased under resale agreements	308,400	183,700
Securities borrowed	106,900	102,100
Investment securities, held-to-maturity	31,400	47,700
Loans, net of allowance for loan losses	968,000	914,600
Other	60,500	53,900
Financial liabilities
Deposits	1,447,400	1,422,700
Federal funds purchased and securities loaned or sold under repurchase agreements	181,400	158,200
Short-term borrowings	62,100	42,600
Accounts payable and other liabilities	160,600	152,000
Beneficial interests issued by consolidated VIEs	20,200	26,000
Long-term debt and junior subordinated deferrable interest debentures	227,100	236,600
Wholesale lending-related commitments	1,000	1,100
Fair value
Financial assets
Cash and due from banks	22,300	25,900
Deposits with banks	256,500	405,400
Accrued interest and accounts receivable	72,000	67,000
Federal funds sold and securities purchased under resale agreements	308,400	183,700
Securities borrowed	106,900	102,100
Investment securities, held-to-maturity	31,500	48,700
Loans, net of allowance for loan losses	970,000	920,300
Other	60,600	61,300
Financial liabilities
Deposits	1,447,500	1,422,700
Federal funds purchased and securities loaned or sold under repurchase agreements	181,400	158,200
Short-term borrowings	62,100	42,600
Accounts payable and other liabilities	160,200	151,800
Beneficial interests issued by consolidated VIEs	20,200	26,000
Long-term debt and junior subordinated deferrable interest debentures	227,900	243,500
Wholesale lending-related commitments	2,100	1,600
Fair value | Level 1
Financial assets
Cash and due from banks	22,300	25,900
Deposits with banks	256,500	401,800
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	200	0
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
Fair value | Level 2
Financial assets
Cash and due from banks	0	0
Deposits with banks	0	3,600
Accrued interest and accounts receivable	71,900	67,000
Federal funds sold and securities purchased under resale agreements	308,400	183,700
Securities borrowed	106,900	102,100
Investment securities, held-to-maturity	31,500	48,700
Loans, net of allowance for loan losses	241,500	213,200
Other	59,600	52,100
Financial liabilities
Deposits	1,447,500	1,422,700
Federal funds purchased and securities loaned or sold under repurchase agreements	181,400	158,200
Short-term borrowings	62,100	42,400
Accounts payable and other liabilities	157,000	148,900
Beneficial interests issued by consolidated VIEs	20,200	26,000
Long-term debt and junior subordinated deferrable interest debentures	224,600	240,300
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	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	728,500	707,100
Other	1,000	9,200
Financial liabilities
Deposits	0	0
Federal funds purchased and securities loaned or sold under repurchase agreements	0	0
Short-term borrowings	0	200
Accounts payable and other liabilities	3,000	2,900
Beneficial interests issued by consolidated VIEs	0	0
Long-term debt and junior subordinated deferrable interest debentures	3,300	3,200
Wholesale lending-related commitments	$ 2,100	$ 1,600