Fair Value - Carrying Value and Estimated Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Financial Assets:
Cash and due from banks	$ 1,314	$ 1,207	$ 1,855	$ 3,220
Interest-bearing deposits with banks	70,935	75,338
Securities purchased under resale agreements	1,956	3,404
Held to maturity, fair value	34,994	29,798
Financial Liabilities:
Noninterest-bearing	59,397	65,800
Interest-bearing—U.S.	30,911	29,958
Interest-bearing—non-U.S.	96,855	95,869
Securities sold under repurchase agreements	4,400	4,499
Other short-term borrowings	1,585	1,754
Reported Amount
Financial Assets:
Cash and due from banks	1,314	1,207
Interest-bearing deposits with banks	70,935	75,338
Securities purchased under resale agreements	1,956	3,404
Held to maturity, fair value	35,169	29,952
Net loans (excluding leases)	18,862	17,838
Financial Liabilities:
Noninterest-bearing	59,397	65,800
Interest-bearing—U.S.	30,911	29,958
Interest-bearing—non-U.S.	96,855	95,869
Securities sold under repurchase agreements	4,400	4,499
Other short-term borrowings	1,585	1,754
Long-term debt	11,430	11,497
Estimated Fair Value
Financial Assets:
Cash and due from banks	1,314	1,207
Interest-bearing deposits with banks	70,935	75,338
Securities purchased under resale agreements	1,956	3,404
Held to maturity, fair value	34,994	29,798
Net loans (excluding leases)	18,877	17,792
Financial Liabilities:
Noninterest-bearing	59,397	65,800
Interest-bearing—U.S.	30,911	29,958
Interest-bearing—non-U.S.	96,855	95,869
Securities sold under repurchase agreements	4,400	4,499
Other short-term borrowings	1,585	1,754
Long-term debt	11,618	11,604
Estimated Fair Value | Fair Value, Measurements, Nonrecurring
Financial Assets:
Net loans (excluding leases)		14
Estimated Fair Value | Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	1,314	1,207
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Held to maturity, fair value	17,400	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
Other short-term borrowings	0	0
Long-term debt	0	0
Estimated Fair Value | Pricing Methods with Significant Observable Market Inputs (Level 2)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	70,935	75,338
Securities purchased under resale agreements	1,956	3,404
Held to maturity, fair value	17,439	29,798
Net loans (excluding leases)	18,781	17,667
Financial Liabilities:
Noninterest-bearing	59,397	65,800
Interest-bearing—U.S.	30,911	29,958
Interest-bearing—non-U.S.	96,855	95,869
Securities sold under repurchase agreements	4,400	4,499
Other short-term borrowings	1,585	1,754
Long-term debt	11,282	11,215
Estimated Fair Value | 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	155	0
Net loans (excluding leases)	96	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
Other short-term borrowings	0	0
Long-term debt	$ 336	$ 389