Quarterly report pursuant to Section 13 or 15(d)

Equity Method Investments - 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 - 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
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Schedule Of Results Related To Equity Accounted Investees [Line Items]      
Current Assets $ 3   $ 3
Total Assets 115   99
Current Liabilities 4   4
Total Liabilities 38   39
Members' Equity 77   $ 60
Revenue 3 $ 3  
Income from Continuing Operations 1 0  
Net income $ 1 $ 0