Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financial assets
Cash and due from banks	$ 23,225	$ 25,898
Deposits with banks	395,872	405,406
Federal funds sold and securities purchased under resale agreements	217,632	198,422
Securities, held-to-maturity	30,918	48,652
Loans, net of allowance for loan losses	2,987	2,508
Financial liabilities
Beneficial interests issued by consolidated VIEs	20,241	26,081
Carrying value
Financial assets
Cash and due from banks	23,200	25,900
Deposits with banks	395,900	405,400
Accrued interest and accounts receivable	77,700	67,000
Federal funds sold and securities purchased under resale agreements	205,400	183,700
Securities borrowed	117,900	102,100
Securities, held-to-maturity	31,400	47,700
Loans, net of allowance for loan losses	938,200	914,600
Other	55,000	53,900
Financial liabilities
Deposits	1,438,300	1,422,700
Federal funds purchased and securities loaned or sold under repurchase agreements	180,500	158,200
Short-term borrowings	56,700	42,600
Accounts payable and other liabilities	173,400	152,000
Beneficial interests issued by consolidated VIEs	20,200	26,000
Long-term debt and junior subordinated deferrable interest debentures	216,000	236,600
Wholesale lending-related commitments	1,100	1,100
Total estimated fair value
Financial assets
Cash and due from banks	23,200	25,900
Deposits with banks	395,900	405,400
Accrued interest and accounts receivable	77,700	67,000
Federal funds sold and securities purchased under resale agreements	205,400	183,700
Securities borrowed	117,900	102,100
Securities, held-to-maturity	30,900	48,700
Loans, net of allowance for loan losses	937,300	920,300
Other	55,100	61,300
Financial liabilities
Deposits	1,438,400	1,422,700
Federal funds purchased and securities loaned or sold under repurchase agreements	180,500	158,200
Short-term borrowings	56,700	42,600
Accounts payable and other liabilities	173,100	151,800
Beneficial interests issued by consolidated VIEs	20,200	26,000
Long-term debt and junior subordinated deferrable interest debentures	220,800	243,500
Wholesale lending-related commitments	1,500	1,600
Total estimated fair value | Level 1
Financial assets
Cash and due from banks	23,200	25,900
Deposits with banks	392,200	401,800
Accrued interest and accounts receivable	0	0
Federal funds sold and securities purchased under resale agreements	0	0
Securities borrowed	0	0
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	0	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
Total estimated fair value | Level 2
Financial assets
Cash and due from banks	0	0
Deposits with banks	3,700	3,600
Accrued interest and accounts receivable	77,600	67,000
Federal funds sold and securities purchased under resale agreements	205,400	183,700
Securities borrowed	117,900	102,100
Securities, held-to-maturity	30,900	48,700
Loans, net of allowance for loan losses	227,300	213,200
Other	54,100	52,100
Financial liabilities
Deposits	1,438,400	1,422,700
Federal funds purchased and securities loaned or sold under repurchase agreements	180,500	158,200
Short-term borrowings	56,700	42,400
Accounts payable and other liabilities	170,000	148,900
Beneficial interests issued by consolidated VIEs	20,200	26,000
Long-term debt and junior subordinated deferrable interest debentures	217,500	240,300
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	0
Federal funds sold and securities purchased under resale agreements	0	0
Securities borrowed	0	0
Securities, held-to-maturity	0	0
Loans, net of allowance for loan losses	710,000	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	3,100	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	$ 1,500	$ 1,600