Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Financial Assets:
Cash and due from banks	$ 4,673	$ 1,207	$ 3,084	$ 1,855
Interest-bearing deposits with banks	75,169	75,338
Securities purchased under resale agreements	2,010	3,404
Held to maturity, fair value	30,895	29,798
Financial Liabilities:
Noninterest-bearing	57,268	65,800
Interest-bearing—U.S.	33,060	29,958
Interest-bearing—non-U.S.	102,802	95,869
Securities sold under repurchase agreements	4,350	4,499
Federal funds purchased	29	6
Other short-term borrowings	1,683	1,748
Reported Value Measurement
Financial Assets:
Cash and due from banks	4,673	1,207
Interest-bearing deposits with banks	75,169	75,338
Securities purchased under resale agreements	2,010	3,404
Held to maturity, fair value	30,386	29,952
Net loans (excluding leases)	18,962	17,838
Financial Liabilities:
Noninterest-bearing	57,268	65,800
Interest-bearing—U.S.	33,060	29,958
Interest-bearing—non-U.S.	102,802	95,869
Securities sold under repurchase agreements	4,350	4,499
Federal funds purchased	29	6
Other short-term borrowings	1,683	1,748
Long-term debt	11,924	11,497
Estimate of Fair Value Measurement
Financial Assets:
Cash and due from banks	4,673	1,207
Interest-bearing deposits with banks	75,169	75,338
Securities purchased under resale agreements	2,010	3,404
Held to maturity, fair value	30,895	29,798
Net loans (excluding leases)	18,940	17,792
Financial Liabilities:
Noninterest-bearing	57,268	65,800
Interest-bearing—U.S.	33,060	29,958
Interest-bearing—non-U.S.	102,802	95,869
Securities sold under repurchase agreements	4,350	4,499
Federal funds purchased	29	6
Other short-term borrowings	1,683	1,748
Long-term debt	12,033	11,604
Estimate of Fair Value Measurement | Fair Value, Measurements, Nonrecurring
Financial Assets:
Net loans (excluding leases)		14
Estimate of Fair Value Measurement | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,673	1,207
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Held to maturity, fair value	17,928	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
Estimate of Fair Value Measurement | Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	75,169	75,338
Securities purchased under resale agreements	2,010	3,404
Held to maturity, fair value	12,830	29,798
Net loans (excluding leases)	18,836	17,667
Financial Liabilities:
Noninterest-bearing	57,268	65,800
Interest-bearing—U.S.	33,060	29,958
Interest-bearing—non-U.S.	102,802	95,869
Securities sold under repurchase agreements	4,350	4,499
Federal funds purchased	29	6
Other short-term borrowings	1,683	1,748
Long-term debt	11,660	11,215
Estimate of Fair Value Measurement | 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
Held to maturity, fair value	137	0
Net loans (excluding leases)	104	125
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	$ 373	$ 389