Securities - Amortized Cost, Gross Unrealized Gains, Gross Unrealized Losses, and Fair Values of Securities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 20,602	$ 22,626
Gross Unrealized Gains	474	277
Gross Unrealized Losses	169	70
Fair Value	20,907	22,833
U.S. government sponsored agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,599	6,943
Gross Unrealized Gains	30	54
Fair Value	2,629	6,997
U.S. government and government sponsored agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,687	13,307
Gross Unrealized Gains	285	182
Gross Unrealized Losses	2	4
Fair Value	11,970	13,485
Privately issued [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	505	800
Gross Unrealized Gains	10	1
Gross Unrealized Losses	17	63
Fair Value	498	738
Commercial mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,251	1,032
Gross Unrealized Gains	110	29
Gross Unrealized Losses		1
Fair Value	2,361	1,060
Collateralized loan obligations (CLOs) [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,652
Gross Unrealized Gains	4
Gross Unrealized Losses	66
Fair Value	1,590
Other debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,804	463
Gross Unrealized Gains	35	11
Gross Unrealized Losses	84	2
Fair Value	1,755	472
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	104	81
Fair Value	$ 104	$ 81

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 3: http://www.xbrl.org/2003/role/presentationRef

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

-Publisher FASB

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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 6: 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 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-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.

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

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-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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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

-Publisher FASB

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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

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details