Dividends Declared to Stockholders (Detail) (USD $) In Millions, except Per Share data	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Regular Dividend	Mar. 31, 2011 Regular Dividend	Jun. 30, 2011 Regular Dividend	Jun. 30, 2010 Special Dividend	Jun. 30, 2010 Special Dividend
Dividends Payable [Line Items]
Per Share	$ 0.075	$ 1.500	$ 0.150	$ 1.500	$ 0.075	$ 0.075
Cash dividend declared to stockholders					$ 10.9		$ 21.8	$ 232.7	$ 232.7

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770

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