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Amount classified as assets attributable to disposal group held for sale or disposed of, expected to be disposed of after one year or the normal operating cycle, if longer.

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Amount of gain (loss) on sale or disposal of proven and unproven oil and gas properties.

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The cash outflow to purchase of mineral interests in oil and gas properties for use in the normal oil and gas operations and not intended for resale.

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The cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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Acquisitions & Divestitures Haynesville Divestiture (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Business Acquisition [Line Items]
Noncurrent assets held for sale	$ 0.0		$ 0.0		$ 692.7
Payments to acquire oil and gas property			3.6	$ 48.3
Proceeds from Sale of Oil and Gas Property and Equipment			676.5	217.5
Gain (Loss) on Disposition of Oil and Gas Property	(2.1)	$ 27.1	2.5	26.7
Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment			633.9
Gain (Loss) on Disposition of Oil and Gas Property	(0.3)		(1.0)
Results of Operations, (Income) Loss before Income Taxes	$ (0.2)	18.0	3.1	37.7
Restructuring Charges			(1.4)
Haynesville Divestiture [Member] \| Total incurred to date [Member]
Business Acquisition [Line Items]
Gain (Loss) on Disposition of Oil and Gas Property			(4.0)
Uinta Basin [Member]
Business Acquisition [Line Items]
Proceeds from Sale of Oil and Gas Property and Equipment				153.0
Gain (Loss) on Disposition of Oil and Gas Property				(12.4)
Results of Operations, (Income) Loss before Income Taxes		$ (4.4)	$ (0.2)	$ (419.3)
Property, Plant and Equipment [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					683.7
Other Noncurrent Assets [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					7.8
Noncurrent Assets Held for Sale [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					692.7
Other Current Liabilities [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					3.4
Asset Retirement Obligations, Current [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					0.7
Asset Retirement Obligations, Long Term [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					56.9
Derivative Financial Instruments, Liabilities [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					0.3
Other Noncurrent Liabilities [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					61.3
Other Current Assets [Member] \| Haynesville Divestiture [Member]
Business Acquisition [Line Items]
Noncurrent assets held for sale					$ 1.2