XML 163 R129.htm IDEA: XBRL DOCUMENT v3.10.0.1
COMMITMENTS AND CONTINGENCIES - Guarantees and Obligations Narrative (Details) - USD ($)
Feb. 08, 2019
Dec. 31, 2018
Guarantee Of Financial Obligations Of Npt    
Loss Contingencies [Line Items]    
Maximum exposure   $ 25,000,000
Guarantee Of Npt Letters Of Credit    
Loss Contingencies [Line Items]    
Maximum exposure   $ 14,000,000
Subsequent Event | Revolution Wind And South Fork Wind Power    
Loss Contingencies [Line Items]    
Equity Method Investments $ 225,000,000  
Equity method investment, ownership percentage 50.00%  
Parent obligations $ 127,600,000