Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Financial Assets:
Cash and due from banks	$ 3,149	$ 1,855	$ 3,877	$ 3,220
Interest-bearing deposits with banks	83,398	93,523
Securities purchased under resale agreements	11,331	2,390
Investment securities held to maturity, fair value	16,417	17,842
Net loans (excluding leases)	17,339	17,131
Financial Liabilities:
Noninterest-bearing	72,704	70,490
Interest-bearing—U.S.	30,769	33,012
Interest-bearing—non-U.S.	107,879	105,538
Securities sold under repurchase agreements	10,158	8,925
Federal funds purchased	17	21
Other short-term borrowings	4,346	4,381
Long-term debt	9,432	10,229
Reported Amount
Financial Assets:
Cash and due from banks	3,149	1,855
Interest-bearing deposits with banks	83,398	93,523
Securities purchased under resale agreements	11,331	2,390
Investment securities held to maturity, fair value	16,245	17,723
Net loans (excluding leases)	17,344	17,158
Financial Liabilities:
Noninterest-bearing	72,704	70,490
Interest-bearing—U.S.	30,769	33,012
Interest-bearing—non-U.S.	107,879	105,538
Securities sold under repurchase agreements	10,158	8,925
Federal funds purchased	17	21
Other short-term borrowings	4,346	4,381
Long-term debt	9,174	10,042
Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	3,149	1,855
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held to maturity, fair value	0	0
Net loans (excluding leases)	0	0
Financial Liabilities:
Noninterest-bearing	0	0
Interest-bearing—U.S.	0	0
Interest-bearing—non-U.S.	0	0
Securities sold under repurchase agreements	0	0
Federal funds purchased	0	0
Other short-term borrowings	0	0
Long-term debt	0	0
Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	83,398	93,523
Securities purchased under resale agreements	11,331	2,390
Investment securities held to maturity, fair value	16,417	17,842
Net loans (excluding leases)	17,177	16,964
Financial Liabilities:
Noninterest-bearing	72,704	70,490
Interest-bearing—U.S.	30,769	33,012
Interest-bearing—non-U.S.	107,879	105,538
Securities sold under repurchase agreements	10,158	8,925
Federal funds purchased	17	21
Other short-term borrowings	4,346	4,381
Long-term debt	8,592	9,382
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held to maturity, fair value	0	0
Net loans (excluding leases)	162	167
Financial Liabilities:
Noninterest-bearing	0	0
Interest-bearing—U.S.	0	0
Interest-bearing—non-U.S.	0	0
Securities sold under repurchase agreements	0	0
Federal funds purchased	0	0
Other short-term borrowings	0	0
Long-term debt	$ 840	$ 847