CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
OPERATING ACTIVITIES
Net income (loss)	$ (67.9)	$ (389.6)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	251.3	438.7
Deferred income taxes (benefit)	(87.7)	(120.5)
Impairment	5.0	404.4
Non-cash share-based compensation	11.2	16.3
Amortization of debt issuance costs and discounts	2.7	2.6
Net (gain) loss from asset sales, inclusive of restructuring costs	(4.6)	0.4
Unrealized (gains) losses on marketable securities	(2.7)	(0.4)
Unrealized (gains) losses on derivative contracts	121.3	43.6
Changes in operating assets and liabilities	(32.9)	(18.6)
Net Cash Provided by (Used in) Operating Activities	195.7	376.9
INVESTING ACTIVITIES
Property acquisitions	(1.8)	(45.1)
Property, plant and equipment, including exploratory well expense	(316.8)	(764.3)
Proceeds from disposition of assets	666.7	48.8
Net Cash Provided by (Used in) Investing Activities	348.1	(760.6)
FINANCING ACTIVITIES
Checks outstanding in excess of cash balances	(9.3)	(35.5)
Proceeds from credit facility	56.0	2,029.5
Repayments of credit facility	(486.0)	(1,543.5)
Common stock repurchased and retired	0.0	(58.4)
Treasury stock repurchases	(6.3)	(5.9)
Other capital contributions	0.0	0.2
Net Cash Provided by (Used in) Financing Activities	(445.6)	386.4
Change in cash, cash equivalents and restricted cash(1)	98.2	2.7
Beginning cash, cash equivalents and restricted cash(1)	28.1	23.4
Ending cash, cash equivalents and restricted cash(1)	126.3	26.1
Supplemental Disclosures:
Cash paid for interest, net of capitalized interest	63.3	63.5
Cash paid for income taxes, net	1.5	0.2
Cash Paid for Amounts Included in the Measurement of Lease Liabilities	13.1	0.0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	9.8	0.0
Non-cash Investing Activities:
Change in capital expenditure accruals and other non-cash adjustments	$ 20.3	$ 20.2