Fair Value Measurement - Carrying Value and Estimated Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Financial assets
Cash and due from banks	$ 24,095	$ 27,831	$ 27,523	$ 39,771
Deposits with banks	398,807	484,477
Federal funds sold and securities purchased under resale agreements	212,850	215,803
Securities, held-to-maturity	52,697	51,154
Financial liabilities
Commercial paper	42,238	66,344
Beneficial interests issued by consolidated VIEs	50,002	52,362
Carrying value
Financial assets
Cash and due from banks	24,100	27,800
Deposits with banks	398,800	484,500
Accrued interest and accounts receivable	69,600	70,100
Federal funds sold and securities purchased under resale agreements	184,200	187,200
Securities borrowed	98,000	109,400
Securities, held-to-maturity	51,600	49,300
Loans, net of allowance for loan losses	774,900	740,500
Other	65,200	64,700
Financial liabilities
Deposits	1,275,800	1,354,600
Federal funds purchased and securities loaned or sold under repurchase agreements	177,400	189,100
Commercial paper	42,200	66,300
Other borrowed funds	16,100	15,500
Accounts payable and other liabilities	163,500	176,700
Beneficial interests issued by consolidated VIEs	48,700	50,200
Long-term debt and junior subordinated deferrable interest debentures	255,400	246,600
Wholesale lending-related commitments	600	600
Estimate of Fair Value
Financial assets
Cash and due from banks	24,100	27,800
Deposits with banks	398,800	484,500
Accrued interest and accounts receivable	69,600	70,100
Federal funds sold and securities purchased under resale agreements	184,200	187,200
Securities borrowed	98,000	109,400
Securities, held-to-maturity	52,700	51,200
Loans, net of allowance for loan losses	780,000	744,900
Other	69,700	69,000
Financial liabilities
Deposits	1,275,900	1,354,800
Federal funds purchased and securities loaned or sold under repurchase agreements	177,300	189,100
Commercial paper	42,200	66,300
Other borrowed funds	16,100	15,500
Accounts payable and other liabilities	163,300	176,600
Beneficial interests issued by consolidated VIEs	48,700	50,200
Long-term debt and junior subordinated deferrable interest debentures	261,300	255,400
Wholesale lending-related commitments	1,600	1,600
Estimate of Fair Value | Level 1
Financial assets
Cash and due from banks	24,100	27,800
Deposits with banks	395,200	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	0	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
Estimate of Fair Value | Level 2
Financial assets
Cash and due from banks	0	0
Deposits with banks	3,600	4,100
Accrued interest and accounts receivable	69,400	70,000
Federal funds sold and securities purchased under resale agreements	184,200	187,200
Securities borrowed	98,000	109,400
Securities, held-to-maturity	52,700	51,200
Loans, net of allowance for loan losses	22,700	21,800
Other	56,600	55,700
Financial liabilities
Deposits	1,274,700	1,353,600
Federal funds purchased and securities loaned or sold under repurchase agreements	177,300	189,100
Commercial paper	42,200	66,300
Other borrowed funds	16,100	15,500
Accounts payable and other liabilities	160,900	173,700
Beneficial interests issued by consolidated VIEs	46,800	48,200
Long-term debt and junior subordinated deferrable interest debentures	257,300	251,600
Wholesale lending-related commitments	0	0
Estimate of Fair Value | 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	757,300	723,100
Other	13,100	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	2,400	2,900
Beneficial interests issued by consolidated VIEs	1,900	2,000
Long-term debt and junior subordinated deferrable interest debentures	4,000	3,800
Wholesale lending-related commitments	$ 1,600	$ 1,600