Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014	Dec. 31, 2013
Financial Assets:
Cash and due from banks	$ 3,084	$ 1,855	$ 6,247	$ 3,220
Interest-bearing deposits with banks	116,728	93,523
Securities purchased under resale agreements	4,447	2,390
Investment securities held to maturity, fair value	16,198	17,842
Net loans (excluding leases)	17,606	17,131
Financial Liabilities:
Noninterest-bearing	83,120	70,490
Interest-bearing—U.S.	32,839	33,012
Interest-bearing—non-U.S.	114,632	105,538
Securities sold under repurchase agreements	10,978	8,925
Federal funds purchased	15	21
Other short-term borrowings	4,756	4,381
Long-term debt	9,257	10,229
Reported Amount
Financial Assets:
Cash and due from banks	3,084	1,855
Interest-bearing deposits with banks	116,728	93,523
Securities purchased under resale agreements	4,447	2,390
Investment securities held to maturity, fair value	16,155	17,723
Net loans (excluding leases)	17,617	17,158
Financial Liabilities:
Noninterest-bearing	83,120	70,490
Interest-bearing—U.S.	32,839	33,012
Interest-bearing—non-U.S.	114,632	105,538
Securities sold under repurchase agreements	10,978	8,925
Federal funds purchased	15	21
Other short-term borrowings	4,756	4,381
Long-term debt	9,085	10,042
Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	3,084	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	116,728	93,523
Securities purchased under resale agreements	4,447	2,390
Investment securities held to maturity, fair value	16,198	17,842
Net loans (excluding leases)	17,451	16,964
Financial Liabilities:
Noninterest-bearing	83,120	70,490
Interest-bearing—U.S.	32,839	33,012
Interest-bearing—non-U.S.	114,632	105,538
Securities sold under repurchase agreements	10,978	8,925
Federal funds purchased	15	21
Other short-term borrowings	4,756	4,381
Long-term debt	8,451	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)	155	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	$ 806	$ 847