Fair Value (Carrying Value and Estimated Fair Value of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Dec. 31, 2012
Financial Assets:
Cash and due from banks	$ 4,146	$ 3,220	$ 3,896	$ 2,590
Interest-bearing deposits with banks	86,946	64,257
Securities purchased under resale agreements	2,603	6,230
Investment securities held to maturity, fair value	18,865	17,560
Net loans (excluding leases)	17,287	12,355
Financial Liabilities:
Noninterest-bearing	66,134	65,614
Interest-bearing—U.S.	24,435	13,392
Interest-bearing—non-U.S.	117,399	103,262
Securities sold under repurchase agreements	9,385	7,953
Federal funds purchased	17	19
Other short-term borrowings	4,307	3,780
Long-term debt	9,352	9,909
Reported Amount
Financial Assets:
Cash and due from banks	4,146	3,220
Interest-bearing deposits with banks	86,946	64,257
Securities purchased under resale agreements	2,603	6,230
Investment securities held to maturity, fair value	18,767	17,740
Net loans (excluding leases)	17,296	12,363
Financial Liabilities:
Noninterest-bearing	66,134	65,614
Interest-bearing—U.S.	24,435	13,392
Interest-bearing—non-U.S.	117,399	103,262
Securities sold under repurchase agreements	9,385	7,953
Federal funds purchased	17	19
Other short-term borrowings	4,307	3,780
Long-term debt	9,016	9,699
Quoted Market Prices in Active Markets (Level 1)
Financial Assets:
Cash and due from banks	4,146	3,220
Interest-bearing deposits with banks	0	0
Securities purchased under resale agreements	0	0
Investment securities held to maturity, fair value	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)
Financial Assets:
Cash and due from banks	0	0
Interest-bearing deposits with banks	86,946	64,257
Securities purchased under resale agreements	2,603	6,230
Investment securities held to maturity, fair value	18,865	17,560
Net loans (excluding leases)	16,830	11,908
Financial Liabilities:
Noninterest-bearing	66,134	65,614
Interest-bearing—U.S.	24,435	13,392
Interest-bearing—non-U.S.	117,399	103,262
Securities sold under repurchase agreements	9,385	7,953
Federal funds purchased	17	19
Other short-term borrowings	4,307	3,780
Long-term debt	8,474	9,056
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
Investment securities held to maturity, fair value	0	0
Net loans (excluding leases)	457	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	$ 878	$ 853