Fair Value Measurements - Beginning and Ending Balances for Assets Recorded at Fair Value Using Significant Unobservable Inputs (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset, Beginning Balance	$ 18
Fair Value, Recurring Basis, Asset, Gain (Loss) Included in income	0
Fair Value, Recurring Basis, Asset, Gain (Loss) Included in other comprehensive income	(5)
Fair Value, Recurring Basis, Asset, Purchases	0
Fair Value, Recurring Basis, Asset, Issuances	0
Fair Value, Recurring Basis, Asset, Settlement	(13)
Fair Value, Recurring Basis, Asset Transfers Into Level 3	0
Fair Value, Recurring Basis, Asset Transfers Out of Level 3	0
Fair Value, Asset, Ending Balance	0
Fair Value, Assets Measured on Recurring Basis, Unrealized Gain (Loss)	0
Asset-backed securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset, Beginning Balance	18
Fair Value, Recurring Basis, Asset, Gain (Loss) Included in income	0
Fair Value, Recurring Basis, Asset, Gain (Loss) Included in other comprehensive income	(5)
Fair Value, Recurring Basis, Asset, Purchases	0
Fair Value, Recurring Basis, Asset, Issuances	0
Fair Value, Recurring Basis, Asset, Settlement	(13)
Fair Value, Recurring Basis, Asset Transfers Into Level 3	0
Fair Value, Recurring Basis, Asset Transfers Out of Level 3	0
Fair Value, Asset, Ending Balance	0
Fair Value, Assets Measured on Recurring Basis, Unrealized Gain (Loss)	$ 0

Fair Value Assets Measured On Recurring Basis Unrealized Gain (Loss) Included In Other Comprehensive Income

No definition available.

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- Details

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- Definition

Amount of gain (loss) recognized in earnings, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

+ Details

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- Definition

Amount of gain (loss) recognized in other comprehensive income, arising from assets measured at fair value on a recurring basis using unobservable inputs (level 3).

+ References

+ Details

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- Definition

Issues that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

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Period Type:	duration

- Definition

Purchases that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

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Period Type:	duration

- Definition

Settlements that have taken place during the period in relation to assets measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

+ Details

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Period Type:	duration

- Definition

Transfers into assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

+ Details

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Period Type:	duration

- Definition

Transfers out of assets measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-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.

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