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
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Schedule Of Results Related To Equity Accounted Investees [Line Items]    
Current Assets $ 3 $ 2
Total Assets 88 90
Current Liabilities 4 4
Total Liabilities 39 42
Members' Equity 49 48
Revenue 12 13
Income from Continuing Operations 5 6
Net Income $ 5 $ 6