Basis of Presentation - Performance Obligation, Expected Timing (Details) $ in Millions	Jun. 30, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Natural Gas Revenues	$ 188
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-04-01
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Expected timing	6 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-07-01
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Natural Gas Revenues	$ 72
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Expected timing	1 year
Natural Gas Revenues	$ 116