Fair Values of Assets and Liabilities (Details 7) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Financial Assets
Cash and due from banks	$ 9,561	$ 13,962
Investment securities held-to-maturity	21,505	18,877
Loans	207,274	205,082
Other financial instruments	6,226
Financial Liabilities
Deposits	233,553	230,885
Short-term borrowings	27,454	30,468
Long-term debt	30,395	31,953
Carrying Amount [Member]
Financial Assets
Cash and due from banks	9,561	13,962
Federal funds sold and securities purchased under resale agreements	124	64
Investment securities held-to-maturity	21,505	18,877
Mortgages held for sale	2	3
Other loans held for sale	196	228
Loans	207,274	205,082
Other financial instruments	6,105	6,095
Financial Liabilities
Deposits	233,553	230,885
Short-term borrowings	27,454	30,468
Long-term debt	30,395	31,953
Fair Value [Member]
Financial Assets
Cash and due from banks	9,561	13,962
Federal funds sold and securities purchased under resale agreements	124	64
Investment securities held-to-maturity	21,862	19,216
Mortgages held for sale	2	3
Other loans held for sale	197	228
Loans	209,026	206,646
Other financial instruments	6,153	6,140
Financial Liabilities
Deposits	233,930	231,184
Short-term borrowings	27,594	30,448
Long-term debt	30,947	32,664
Fair Value [Member] | Level 1 [Member]
Financial Assets
Cash and due from banks	9,561
Investment securities held-to-maturity	2,447
Fair Value [Member] | Level 2 [Member]
Financial Assets
Federal funds sold and securities purchased under resale agreements	124
Investment securities held-to-maturity	19,321
Other financial instruments	1,268
Financial Liabilities
Deposits	233,930
Short-term borrowings	27,594
Long-term debt	30,947
Fair Value [Member] | Level 3 [Member]
Financial Assets
Investment securities held-to-maturity	94
Mortgages held for sale	2
Other loans held for sale	197
Loans	209,026
Other financial instruments	$ 4,885