Fair Values (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investment securities:
Equity securities	$ 251	$ 296
Debt securities and other	5,542	5,318
Derivative assets	958	942
Total assets	6,751	6,556
Level 1 [Member]
Investment securities:
Equity securities	251	296
Debt securities and other	337	338
Derivative assets	0	0
Total assets	588	634
Level 2 [Member]
Investment securities:
Equity securities	0	0
Debt securities and other	5,205	4,980
Derivative assets	958	942
Total assets	6,163	5,922
Level 3 [Member]
Investment securities:
Total assets	$ 0	$ 0

Amount of equity securities categorized neither as held-to-maturity nor as trading.

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-Name Statement of Financial Accounting Standard (FAS)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 9: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

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-Name Statement of Financial Accounting Standard (FAS)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details