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Asset Retirement Obligations Asset Retirement Obligations ARO Rollforward (Details)
$ in Millions
3 Months Ended
Mar. 31, 2020
USD ($)
Divestitures [Line Items]  
ARO liability at January 1, 2020 $ 100.9
Accretion 0.9
Additions 0.6
Revisions (0.5)
Liabilities related to assets sold (1.3)
Liabilities settled (0.4)
ARO Liability at March 31, 2020 $ 100.2