Details of Holdings of Perpetual Securities (Detail) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Investment Holdings [Line Items]
Amortized Cost	$ 56,407	$ 55,951
Fair Value	57,429	55,890
Perpetual Securities
Investment Holdings [Line Items]
Amortized Cost	7,504	7,827
Fair Value	6,530	7,512
Unrealized Gain (Loss)	(974)	(315)
Perpetual Securities \| A \| Upper Tier II
Investment Holdings [Line Items]
Amortized Cost	3,352	3,279
Fair Value	2,977	3,250
Unrealized Gain (Loss)	(375)	(29)
Perpetual Securities \| A \| Tier I
Investment Holdings [Line Items]
Amortized Cost	628	632
Fair Value	468	568
Unrealized Gain (Loss)	(160)	(64)
Perpetual Securities \| Upper Tier II
Investment Holdings [Line Items]
Amortized Cost	4,986	5,285
Fair Value	4,539	5,091
Unrealized Gain (Loss)	(447)	(194)
Perpetual Securities \| Upper Tier II \| AA
Investment Holdings [Line Items]
Amortized Cost	197	190
Fair Value	195	201
Unrealized Gain (Loss)	(2)	11
Perpetual Securities \| Upper Tier II \| BBB
Investment Holdings [Line Items]
Amortized Cost	1,174	1,274
Fair Value	1,104	1,164
Unrealized Gain (Loss)	(70)	(110)
Perpetual Securities \| Upper Tier II \| BB or Lower
Investment Holdings [Line Items]
Amortized Cost	263	542
Fair Value	263	476
Unrealized Gain (Loss)	0	(66)
Perpetual Securities \| Tier I
Investment Holdings [Line Items]
Amortized Cost	2,518	2,542
Fair Value	1,991	2,421
Unrealized Gain (Loss)	(527)	(121)
Perpetual Securities \| Tier I \| BBB
Investment Holdings [Line Items]
Amortized Cost	1,175	1,386
Fair Value	974	1,296
Unrealized Gain (Loss)	(201)	(90)
Perpetual Securities \| Tier I \| BB or Lower
Investment Holdings [Line Items]
Amortized Cost	715	524
Fair Value	549	557
Unrealized Gain (Loss)	$ (166)	$ 33

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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

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Reference 4: 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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 5: http://www.xbrl.org/2003/role/presentationRef

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

-Publisher FASB

-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 7: http://www.xbrl.org/2003/role/presentationRef

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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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+ Details