Subsequent Events (Detail) (USD $) In Billions, except Share data	0 Months Ended
Jul. 15, 2011
Subsequent Event [Line Items]
Subsequent event description	On July 11, 2011, the Company entered into an underwriting agreement pursuant to which it sold 138,000,000 shares of its common stock for net proceeds following expenses of approximately $2.4 billion. This transaction settled on July 15, 2011.
Net proceeds from common stock offering	$ 2.4
Common stock sold, shares	138,000,000

Describes the event or transaction that occurred between the balance sheet date and the date the financial statements are issued or available to be issued.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 5
-Paragraph 11
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 855
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6842918&loc=SL6314017-165662

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 165
-Paragraph 13
-Subparagraph a
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration