CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
OPERATING ACTIVITIES
Net income (loss)	$ 119.0	$ (1,111.7)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Depreciation, depletion and amortization	560.2	667.5
Deferred income taxes	68.5	(581.1)
Impairment	28.4	1,188.2
Bargain purchase gain from acquisition	0.4	(4.4)
Other non-cash activity	(9.4)	0.0
Dry hole exploratory well expense	21.2	0.0
Share-based compensation	13.5	29.0
Amortization of debt issuance costs and discounts	4.8	4.8
Net (gain) loss from asset sales	(205.2)	(5.0)
Unrealized (gains) losses on marketable securities	(2.1)	(1.2)
Unrealized (gains) losses on derivative contracts	(161.6)	218.6
Changes in operating assets and liabilities	44.1	128.2
Net Cash Provided by (Used in) Operating Activities	481.8	532.9
INVESTING ACTIVITIES
Property acquisitions	(94.5)	(39.9)
Acquisition deposit held in escrow	(36.6)	(30.0)
Property, plant and equipment, including dry exploratory well expense	(779.6)	(411.2)
Proceeds from disposition of assets	787.9	28.9
Net Cash Provided by (Used in) Investing Activities	(122.8)	(452.2)
FINANCING ACTIVITIES
Checks outstanding in excess of cash balances	(12.3)	(25.5)
Repayments of senior notes	0.0	(176.8)
Long-term debt issuance costs paid	(1.1)	0.0
Proceeds from credit facility	2.0	0.0
Repayments of credit facility	(2.0)	0.0
Treasury stock repurchases	(6.8)	(4.1)
Proceeds from issuance of common stock, net	0.0	781.6
Excess tax (provision) benefit on share-based compensation	0.0	0.2
Net Cash Provided by (Used in) Financing Activities	(20.2)	575.4
Change in cash and cash equivalents	338.8	656.1
Beginning cash and cash equivalents	443.8	376.1
Ending cash and cash equivalents	782.6	1,032.2
Supplemental Disclosures:
Cash paid for interest, net of capitalized interest	96.6	107.0
Cash paid (refund received) for income taxes	0.5	(123.3)
Non-cash Investing Activities
Change in capital expenditure accruals and other non-cash adjustments	$ 68.0	$ (20.4)