Fair Value (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011
Financial Assets:
Cash and due from banks	$ 3,896	$ 2,590	$ 6,432	$ 2,193
Interest-bearing deposits with banks	38,636	50,763
Securities purchased under resale agreements	5,827	5,016
Investment securities held to maturity	16,698	11,379
Financial Liabilities:
Noninterest-bearing	45,679	44,445
Interest-bearing—U.S.	6,575	19,201
Interest-bearing—non-U.S.	101,945	100,535
Securities sold under repurchase agreements	10,123	8,006
Federal funds purchased	94	399
Other short-term borrowings	3,657	4,502
Long-term debt	8,748	7,429
Reported Amount
Financial Assets:
Cash and due from banks	3,896	2,590
Interest-bearing deposits with banks	38,636	50,763
Securities purchased under resale agreements	5,827	5,016
Investment securities held to maturity	16,698	11,379
Loans (excluding leases)	14,445	11,121
Financial Liabilities:
Noninterest-bearing	45,679	44,445
Interest-bearing—U.S.	6,575	19,201
Interest-bearing—non-U.S.	101,945	100,535
Securities sold under repurchase agreements	10,123	8,006
Federal funds purchased	94	399
Other short-term borrowings	3,657	4,502
Long-term debt	8,748	7,429
Estimated Fair Value
Financial Assets:
Cash and due from banks	3,896	2,590
Interest-bearing deposits with banks	38,636	50,763
Securities purchased under resale agreements	5,827	5,016
Investment securities held to maturity	16,543	11,661
Loans (excluding leases)	14,431	11,166
Financial Liabilities:
Noninterest-bearing	45,679	44,445
Interest-bearing—U.S.	6,575	19,201
Interest-bearing—non-U.S.	101,945	100,535
Securities sold under repurchase agreements	10,123	8,006
Federal funds purchased	94	399
Other short-term borrowings	3,657	4,502
Long-term debt	9,101	7,780
Quoted Market Prices in Active Markets (Level 1) | Estimated Fair Value
Financial Assets:
Cash and due from banks	3,896	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:
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	38,636	50,763
Securities purchased under resale agreements	5,827	5,016
Investment securities held to maturity	16,543	11,661
Loans (excluding leases)	13,968	10,276
Financial Liabilities:
Noninterest-bearing	45,679	44,445
Interest-bearing—U.S.	6,575	19,201
Interest-bearing—non-U.S.	101,945	100,535
Securities sold under repurchase agreements	10,123	8,006
Federal funds purchased	94	399
Other short-term borrowings	3,657	4,502
Long-term debt	8,125	6,871
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
Loans (excluding leases)	463	890
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	$ 976	$ 909