Fair Value (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Financial Assets:
Cash and due from banks	$ 4,708	$ 2,590	$ 1,383	$ 2,193
Interest-bearing deposits with banks	39,224	50,763
Securities purchased under resale agreements	8,703	5,016
Investment securities held to maturity	13,593	11,379
Financial Liabilities:
Deposits, Noninterest-bearing	40,704	44,445
Deposits, Interest-bearing - U.S.	11,706	19,201
Deposits, Interest-bearing - Non-U.S.	102,365	100,535
Securities sold under repurchase agreements	11,538	8,006
Federal funds purchased	570	399
Other short-term borrowings	4,354	4,502
Long-term debt	7,440	7,429
Reported Amount
Financial Assets:
Cash and due from banks	4,708	2,590
Interest-bearing deposits with banks	39,224	50,763
Securities purchased under resale agreements	8,703	5,016
Investment securities held to maturity	13,593	11,379
Loans (excluding leases)	12,826	11,121
Financial Liabilities:
Deposits, Noninterest-bearing	40,704	44,445
Deposits, Interest-bearing - U.S.	11,706	19,201
Deposits, Interest-bearing - Non-U.S.	102,365	100,535
Securities sold under repurchase agreements	11,538	8,006
Federal funds purchased	570	399
Other short-term borrowings	4,354	4,502
Long-term debt	7,440	7,429
Fair Value
Financial Assets:
Cash and due from banks	4,708	2,590
Interest-bearing deposits with banks	39,224	50,763
Securities purchased under resale agreements	8,703	5,016
Investment securities held to maturity	13,869	11,661
Loans (excluding leases)	12,881	11,166
Financial Liabilities:
Deposits, Noninterest-bearing	40,704	44,445
Deposits, Interest-bearing - U.S.	11,706	19,201
Deposits, Interest-bearing - Non-U.S.	102,365	100,535
Securities sold under repurchase agreements	11,538	8,006
Federal funds purchased	570	399
Other short-term borrowings	4,354	4,502
Long-term debt	6,837	6,780
Quoted Market Prices in Active Markets (Level 1) | Fair Value
Financial Assets:
Cash and due from banks	4,708	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	39,224	50,763
Securities purchased under resale agreements	8,703	5,016
Investment securities held to maturity	13,869	11,661
Loans (excluding leases)	12,032	10,276
Financial Liabilities:
Deposits, Noninterest-bearing	40,704	44,445
Deposits, Interest-bearing - U.S.	11,706	19,201
Deposits, Interest-bearing - Non-U.S.	102,365	100,535
Securities sold under repurchase agreements	11,538	8,006
Federal funds purchased	570	399
Other short-term borrowings	4,354	4,502
Long-term debt	5,882	5,871
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)	849	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	$ 955	$ 909