Annual report pursuant to Section 13 and 15(d)

Supplemental Oil and Gas Disclosures - Capitalized Costs Related to Oil and Natural Gas (Details)

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Supplemental Oil and Gas Disclosures - Capitalized Costs Related to Oil and Natural Gas (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Net capitalized cost:      
Proved oil and natural gas properties and equipment $ 8,169.9 $ 8,102.0 $ 7,932.5
Accumulated depreciation, depletion and amortization related to oil, NGLs and natural gas activities (7,665.1) (7,525.0) (7,387.8)
Net capitalized costs related to producing activities $ 504.8 $ 577.0 $ 544.7