Annual report pursuant to Section 13 and 15(d)

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

v3.6.0.2
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
 9 Months Ended 12 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Dec. 31, 2014
Schedule Of Results Related To Equity Accounted Investees [Line Items]      
Current Assets $ 62 $ 72  
Total Assets 1,716 1,724  
Current Liabilities 25 18  
Total Liabilities 110 68  
Members' Equity 1,606 1,656  
Revenue 121 152 $ 154
Income from Continuing Operations (3) 24 44
Net Income $ (3) $ 24 $ 44