Fair value measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Financial assets
Cash and due from banks	$ 21,258	$ 27,831	$ 25,372	$ 39,771
Deposits with banks	376,196	484,477
Federal funds sold and securities purchased under resale agreements	218,467	215,803
Securities, held-to-maturity	51,845	51,154
Financial liabilities
Commercial paper	19,656	66,344
Beneficial interests issued by consolidated VIEs	48,733	52,362
Carrying value
Financial assets
Cash and due from banks	21,300	27,800
Deposits with banks	376,200	484,500
Accrued interest and accounts receivable	57,900	70,100
Federal funds sold and securities purchased under resale agreements	191,100	187,200
Securities borrowed	105,300	109,400
Securities, held-to-maturity	50,200	49,300
Loans, net of allowance for loan losses	792,900	740,500
Other	66,700	64,700
Financial liabilities
Deposits	1,262,000	1,354,600
Federal funds purchased and securities loaned or sold under repurchase agreements	176,700	189,100
Commercial paper	19,700	66,300
Other borrowed funds	17,500	15,500
Accounts payable and other liabilities	152,200	172,600
Beneficial interests issued by consolidated VIEs	47,500	50,200
Long-term debt and junior subordinated deferrable interest debentures	261,700	246,600
Wholesale lending-related commitments	700	600
Estimated fair value hierarchy
Financial assets
Cash and due from banks	21,300	27,800
Deposits with banks	376,200	484,500
Accrued interest and accounts receivable	57,900	70,100
Federal funds sold and securities purchased under resale agreements	191,100	187,200
Securities borrowed	105,300	109,400
Securities, held-to-maturity	51,800	51,200
Loans, net of allowance for loan losses	797,600	744,900
Other	71,300	69,000
Financial liabilities
Deposits	1,262,200	1,354,800
Federal funds purchased and securities loaned or sold under repurchase agreements	176,700	189,100
Commercial paper	19,700	66,300
Other borrowed funds	17,500	15,500
Accounts payable and other liabilities	152,000	172,500
Beneficial interests issued by consolidated VIEs	47,500	50,200
Long-term debt and junior subordinated deferrable interest debentures	267,800	255,400
Wholesale lending-related commitments	2,600	1,600
Estimated fair value hierarchy | Level 1
Financial assets
Cash and due from banks	21,300	27,800
Deposits with banks	372,000	480,400
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	100	0
Financial liabilities
Deposits	0	0
Federal funds purchased and securities loaned or sold under repurchase agreements	0	0
Commercial paper	0	$ 0
Other borrowed funds	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
Estimated fair value hierarchy | Level 2
Financial assets
Cash and due from banks	0	0
Deposits with banks	4,200	4,100
Accrued interest and accounts receivable	57,700	70,000
Federal funds sold and securities purchased under resale agreements	191,100	187,200
Securities borrowed	105,300	109,400
Securities, held-to-maturity	51,800	51,200
Loans, net of allowance for loan losses	20,700	21,800
Other	57,700	55,700
Financial liabilities
Deposits	1,261,000	1,353,600
Federal funds purchased and securities loaned or sold under repurchase agreements	176,700	189,100
Commercial paper	19,700	66,300
Other borrowed funds	17,500	15,500
Accounts payable and other liabilities	149,500	169,600
Beneficial interests issued by consolidated VIEs	45,700	48,200
Long-term debt and junior subordinated deferrable interest debentures	263,800	251,600
Wholesale lending-related commitments	0	0
Estimated fair value hierarchy | Level 3
Financial assets
Cash and due from banks	0	0
Deposits with banks	0	0
Accrued interest and accounts receivable	200	100
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	776,900	723,100
Other	13,500	13,300
Financial liabilities
Deposits	1,200	1,200
Federal funds purchased and securities loaned or sold under repurchase agreements	0	0
Commercial paper	0	0
Other borrowed funds	0	0
Accounts payable and other liabilities	2,500	2,900
Beneficial interests issued by consolidated VIEs	1,800	2,000
Long-term debt and junior subordinated deferrable interest debentures	4,000	3,800
Wholesale lending-related commitments	$ 2,600	$ 1,600