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
 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Schedule Of Results Related To Equity Accounted Investees [Line Items]      
Current Assets $ 57   $ 72
Total Assets 1,651   1,724
Current Liabilities 18   18
Total Liabilities 68   68
Members' Equity 1,583   $ 1,656
Revenue 66 $ 77  
Income from Continuing Operations (5) 21  
Net Income $ (5) $ 21