Fair Value (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011
Financial Assets:
Cash and due from banks	$ 5,479	$ 2,590	$ 6,088	$ 2,193
Interest-bearing deposits with banks	44,783	50,763
Securities purchased under resale agreements	5,569	5,016
Investment securities held to maturity	15,468	11,379
Financial Liabilities:
Deposits, Noninterest-bearing	49,922	44,445
Deposits, Interest-bearing - U.S.	7,684	19,201
Deposits, Interest-bearing - Non-U.S.	108,914	100,535
Securities sold under repurchase agreements	9,154	8,006
Federal funds purchased	98	399
Other short-term borrowings	3,277	4,502
Long-term debt	8,841	7,429
Reported Amount
Financial Assets:
Cash and due from banks	5,479	2,590
Interest-bearing deposits with banks	44,783	50,763
Securities purchased under resale agreements	5,569	5,016
Investment securities held to maturity	15,468	11,379
Loans (excluding leases)	15,298	11,121
Financial Liabilities:
Deposits, Noninterest-bearing	49,922	44,445
Deposits, Interest-bearing - U.S.	7,684	19,201
Deposits, Interest-bearing - Non-U.S.	108,914	100,535
Securities sold under repurchase agreements	9,154	8,006
Federal funds purchased	98	399
Other short-term borrowings	3,277	4,502
Long-term debt	8,841	7,429
Fair Value
Financial Assets:
Cash and due from banks	5,479	2,590
Interest-bearing deposits with banks	44,783	50,763
Securities purchased under resale agreements	5,569	5,016
Investment securities held to maturity	15,382	11,661
Loans (excluding leases)	15,291	11,166
Financial Liabilities:
Deposits, Noninterest-bearing	49,922	44,445
Deposits, Interest-bearing - U.S.	7,684	19,201
Deposits, Interest-bearing - Non-U.S.	108,914	100,535
Securities sold under repurchase agreements	9,154	8,006
Federal funds purchased	98	399
Other short-term borrowings	3,277	4,502
Long-term debt	9,145	7,780
Quoted Market Prices in Active Markets (Level 1) | Fair Value
Financial Assets:
Cash and due from banks	5,479	2,590
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held to maturity	0	0
Loans (excluding leases)	0	0
Financial Liabilities:
Deposits, Noninterest-bearing	0	0
Deposits, Interest-bearing - U.S.	0	0
Deposits, 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) | Fair Value
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	44,783	50,763
Securities purchased under resale agreements	5,569	5,016
Investment securities held to maturity	15,382	11,661
Loans (excluding leases)	14,791	10,276
Financial Liabilities:
Deposits, Noninterest-bearing	49,922	44,445
Deposits, Interest-bearing - U.S.	7,684	19,201
Deposits, Interest-bearing - Non-U.S.	108,914	100,535
Securities sold under repurchase agreements	9,154	8,006
Federal funds purchased	98	399
Other short-term borrowings	3,277	4,502
Long-term debt	8,195	6,871
Pricing Methods with Significant Unobservable Market Inputs (Level 3) | 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
Loans (excluding leases)	500	890
Financial Liabilities:
Deposits, Noninterest-bearing	0	0
Deposits, Interest-bearing - U.S.	0	0
Deposits, 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	$ 950	$ 909