CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
OPERATING ACTIVITIES
Net income (loss)	$ (389.6)	$ 122.3
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	438.7	383.3
Deferred income taxes (benefit)	(120.5)	67.2
Impairment	404.4	0.1
Share-based compensation	23.4	7.7
Amortization of debt issuance costs and discounts	2.6	3.1
Bargain purchase gain from acquisition	0.0	0.4
Net (gain) loss from asset sales, inclusive of restructuring costs	0.4	(19.8)
Unrealized (gains) losses on marketable securities	(0.4)	(1.4)
Unrealized (gains) losses on derivative contracts	43.6	(277.6)
Changes in operating assets and liabilities	(25.7)	10.7
Net Cash Provided by (Used in) Operating Activities	376.9	296.0
INVESTING ACTIVITIES
Property acquisitions	(45.1)	(76.6)
Property, plant and equipment, including exploratory well expense	(764.3)	(477.9)
Proceeds from disposition of assets	48.8	2.3
Net Cash Provided by (Used in) Investing Activities	(760.6)	(552.2)
FINANCING ACTIVITIES
Checks outstanding in excess of cash balances	(35.5)	(0.5)
Long-term debt issuance costs paid	0.0	(1.1)
Proceeds from credit facility	2,029.5	0.0
Repayments of credit facility	(1,543.5)	0.0
Common stock repurchased and retired	(58.4)	0.0
Treasury stock repurchases	(5.9)	(6.4)
Other capital contributions	0.2	0.0
Net Cash Provided by (Used in) Financing Activities	386.4	(8.0)
Change in cash, cash equivalents and restricted cash	2.7	(264.2)
Beginning cash, cash equivalents and restricted cash(1)	23.4	465.4
Ending cash, cash equivalents and restricted cash(1)	26.1	201.2
Supplemental Disclosures:
Cash paid for interest, net of capitalized interest	63.5	64.3
Cash paid for income taxes, net	0.2	0.0
Non-cash Investing Activities:
Change in capital expenditure accruals and other non-cash adjustments	$ 20.2	$ 42.4