Fair Value (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Financial Assets:
Cash and due from banks	$ 3,877	$ 3,220	$ 4,708	$ 2,590
Interest-bearing deposits with banks	75,796	64,257
Securities purchased under resale agreements	6,087	6,230
Investment securities held to maturity	18,342	17,740
Financial Liabilities:
Noninterest-bearing	72,800	65,614
Interest-bearing—U.S.	15,327	13,392
Interest-bearing—non-U.S.	106,521	103,262
Securities sold under repurchase agreements	8,953	7,953
Federal funds purchased	18	19
Other short-term borrowings	3,811	3,780
Long-term debt	9,503	9,699
Reported Amount
Financial Assets:
Cash and due from banks	3,877	3,220
Interest-bearing deposits with banks	75,796	64,257
Securities purchased under resale agreements	6,087	6,230
Investment securities held to maturity	18,342	17,740
Net loans (excluding leases)	14,994	12,363
Financial Liabilities:
Noninterest-bearing	72,800	65,614
Interest-bearing—U.S.	15,327	13,392
Interest-bearing—non-U.S.	106,521	103,262
Securities sold under repurchase agreements	8,953	7,953
Federal funds purchased	18	19
Other short-term borrowings	3,811	3,780
Long-term debt	9,503	9,699
Estimated Fair Value
Financial Assets:
Cash and due from banks	3,877	3,220
Interest-bearing deposits with banks	75,796	64,257
Securities purchased under resale agreements	6,087	6,230
Investment securities held to maturity	18,326	17,560
Net loans (excluding leases)	15,002	12,355
Financial Liabilities:
Noninterest-bearing	72,800	65,614
Interest-bearing—U.S.	15,327	13,392
Interest-bearing—non-U.S.	106,521	103,262
Securities sold under repurchase agreements	8,953	7,953
Federal funds purchased	18	19
Other short-term borrowings	3,811	3,780
Long-term debt	9,809	9,909
Quoted Market Prices in Active Markets (Level 1) | Estimated Fair Value
Financial Assets:
Cash and due from banks	3,877	3,220
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held to maturity	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) | Estimated Fair Value
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	75,796	64,257
Securities purchased under resale agreements	6,087	6,230
Investment securities held to maturity	18,326	17,560
Net loans (excluding leases)		11,908
Financial Liabilities:
Noninterest-bearing	72,800	65,614
Interest-bearing—U.S.	15,327	13,392
Interest-bearing—non-U.S.	106,521	103,262
Securities sold under repurchase agreements	8,953	7,953
Federal funds purchased	18	19
Other short-term borrowings	3,811	3,780
Long-term debt	8,927	9,056
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Estimated Fair Value
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	0	0
Net loans (excluding leases)	472	447
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	$ 882	$ 853