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Impact Of ASC Topic 810 On Accounting For Whitehall Group (Detail) (USD $)
12 Months Ended
Dec. 31, 2011
Dec. 31, 2010
Dec. 31, 2011
Whitehall Group [Member]
Dec. 31, 2010
Accounting Standard Codification 810 [Member]
Whitehall Group [Member]
Dec. 31, 2009
Accounting Standard Codification 810 [Member]
Whitehall Group [Member]
Schedule Of Impact Of Accounting Standard Committee On Subsidiary [Line Items]          
Accounting treatment changed from consolidation to the equity method of accounting, voting interest percentage     49.00%    
Net assets decrease         $ 108,000,000
Liabilities decrease         85,000,000
Non-controlling interest decrease         $ 23,000,000
Ownership percentage of the company 10.00% 80.00%   80.00%