Quarterly report pursuant to Section 13 or 15(d)

Equity Method Investments in Affiliate - Summary of Consolidated Financial Position and Results of Operations of Significant Holding Companies, Accounted for Using Equity Method (Detail)

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Equity Method Investments in Affiliate - Summary of Consolidated Financial Position and Results of Operations of Significant Holding Companies, Accounted for Using Equity Method (Detail) - Strong Upwind Holdings LLC [Member] - USD ($)
$ in Millions
 3 Months Ended 12 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Schedule Of Results Related To Equity Accounted Investees [Line Items]        
Current Assets $ 56   $ 61  
Total Assets 1,379   1,409  
Current Liabilities 15   14  
Total Liabilities 59   58  
Members' Equity 1,320   1,351  
Revenue 39 $ 40 149 $ 154
Income from Continuing Operations 5 14 33 44
Net Income $ 5 $ 14 $ 33 $ 44