Securities - Summary of Gross Unrealized Losses and Related Fair Values (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 security
Schedule of Available-for-sale Securities [Line Items]
Number of Securities (Less Than One Year)	28
Gross Unrealized Losses (Less Than One Year)	$ (1)
Aggregate Fair Value of Investments (Less Than One Year)	46
Number of Securities (Greater Than One Year)	0
Gross Unrealized Losses (Greater Than One Year)	0
Aggregate Fair Value of Investments (Greater Than One Year)	0
U.S. corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities (Less Than One Year)	17
Gross Unrealized Losses (Less Than One Year)	(1)
Aggregate Fair Value of Investments (Less Than One Year)	26
Number of Securities (Greater Than One Year)	0
Gross Unrealized Losses (Greater Than One Year)	0
Aggregate Fair Value of Investments (Greater Than One Year)	0
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities (Less Than One Year)	10
Gross Unrealized Losses (Less Than One Year)	0
Aggregate Fair Value of Investments (Less Than One Year)	15
Number of Securities (Greater Than One Year)	0
Gross Unrealized Losses (Greater Than One Year)	0
Aggregate Fair Value of Investments (Greater Than One Year)	0
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of Securities (Less Than One Year)	1
Gross Unrealized Losses (Less Than One Year)	0
Aggregate Fair Value of Investments (Less Than One Year)	5
Number of Securities (Greater Than One Year)	0
Gross Unrealized Losses (Greater Than One Year)	0
Aggregate Fair Value of Investments (Greater Than One Year)	$ 0

Available for sale securities continuous unrealized loss position less than 12 months number of securities.

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- Definition

Available for sale securities continuous unrealized loss position twelve months or longer number of securities.

+ References

No definition available.

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- Definition

Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities which are categorized neither as held-to-maturity nor trading securities.

+ References

No definition available.

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- Definition

Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for securities categorized neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 6

-Subparagraph (a)(2)

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-Name Accounting Standards Codification

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- Definition

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

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

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 03-1

-Paragraph 21

-Subparagraph a(2)

-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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

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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.

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