CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012
OPERATING ACTIVITIES
Net (loss) income	$ 176.1	$ 156.2
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	504.0	413.7
Deferred income taxes	121.0	77.1
Impairment	0.2	61.9
Share-based compensation	13.2	12.3
Amortization of debt issuance costs and discounts	3.1	2.4
Dry exploratory well expense	0	0.1
Net gain from asset sales	(100.2)	(1.5)
Income from unconsolidated affiliates	(2.9)	(3.3)
Distributions from unconsolidated affiliates and other	4.1	3.5
Non-cash loss on early extinguishment of debt	0	0.1
Unrealized loss (gain) on derivative contracts	1.4	(89.9)
Changes in operating assets and liabilities	(222.1)	61.7
Net Cash Provided by Operating Activities	497.9	694.3
INVESTING ACTIVITIES
Property acquisitions	(22.0)	(4.0)
Property, plant and equipment, including dry exploratory well expense	(719.9)	(681.5)
Proceeds from disposition of assets	143.0	3.6
Net Cash Used in Investing Activities	(598.9)	(681.9)
FINANCING ACTIVITIES
Checks outstanding in excess of cash balances	55.8	(29.4)
Long-term debt issued	0	800.0
Long-term debt issuance costs paid	0	(8.8)
Long-term debt repaid	0	6.7
Proceeds from credit facility	898.5	194.5
Repayments of credit facility	(700.0)	(801.0)
Payments for Repurchase of Common Stock	(7.5)	(9.8)
Other capital contributions	2.9	3.4
Dividends paid	(7.2)	(7.1)
Excess tax benefit on share-based compensation	1.3	2.0
Distribution to noncontrolling interest	(3.1)	(3.1)
Net Cash Provided by Financing Activities	240.7	134.0
Change in cash and cash equivalents	139.7	146.4
Beginning cash and cash equivalents	0	0
Ending cash and cash equivalents	139.7	146.4
Supplemental Disclosures:
Cash paid for interest, net of capitalized interest	76.7	42.7
Cash paid (received) for income taxes	41.5	8.0
Non-cash investing activities
Change in capital expenditure accrual balance	$ 2.8	$ 45.3