Quarterly report pursuant to Section 13 or 15(d)

Contingencies (Details)

v3.10.0.1
Contingencies (Details)
$ in Millions
4 Months Ended 6 Months Ended 11 Months Ended 25 Months Ended
Nov. 30, 2017
MMBTU / d
Jun. 30, 2018
USD ($)
MMBTU / d
contract
lawsuit
Dec. 31, 2018
MMBTU / d
Jan. 31, 2018
MMBTU / d
Jan. 01, 2019
MMBTU / d
Mar. 31, 2017
USD ($)
SJGC            
Contingencies            
Natural gas long term purchase contract volume (in MMBtu)/day   80,000        
WGL            
Contingencies            
Natural gas long term purchase contract volume (in MMBtu)/day 600,000   200,000 500,000    
Natural gas long term purchase contract volume increase after specified events (in MMBtu)/day         330,000  
Natural gas long term purchase contract volume after specified events (in MMBtu)/day         530,000  
WGL | Pending Litigation | Minimum            
Contingencies            
Damages sought | $           $ 30
Potential Positive Outcome of Litigation | SJGC            
Contingencies            
Number of lawsuits | lawsuit   2        
Number of long term gas contracts | contract   2        
Potential Positive Outcome of Litigation | SJGC | Pending Litigation            
Contingencies            
Additional accounts receivable | $   $ 79        
Potential Positive Outcome of Litigation | WGL            
Contingencies            
Additional accounts receivable | $   $ 106