CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current Assets
Cash and cash equivalents	$ 139.7	$ 0
Accounts receivable, net	489.8	387.5
Fair value of derivative contracts	104.1	188.7
Gas, oil and NGL inventories at lower of average cost or market	3.8	13.1
Prepaid expenses and other	49.3	68.0
Deferred income taxes	6.4	0
Total Current Assets	793.1	657.3
Property, Plant and Equipment (successful efforts method for gas and oil properties)
Proved properties	10,802.2	10,234.3
Unproved properties	919.8	937.9
Midstream field services	1,650.5	1,634.9
Marketing and other	77.0	64.6
Material and supplies	62.3	61.9
Total Property, Plant and Equipment	13,511.8	12,933.6
Less Accumulated Depreciation, Depletion and Amortization
Exploration and production	4,624.8	4,258.1
Midstream field services	382.1	357.9
Marketing and other	21.0	18.1
Total Accumulated Depreciation, Depletion and Amortization	5,027.9	4,634.1
Net Property, Plant and Equipment	8,483.9	8,299.5
Investment in unconsolidated affiliates	40.0	41.2
Goodwill	59.5	59.5
Fair value of derivative contracts	18.9	4.1
Other noncurrent assets	51.7	46.9
TOTAL ASSETS	9,447.1	9,108.5
Current Liabilities
Checks outstanding in excess of cash balances	95.5	39.7
Accounts payable and accrued expenses	496.7	643.4
Production and property taxes	50.7	41.8
Interest payable	38.0	36.9
Fair value of derivative contracts	2.5	2.6
Deferred income taxes	0	5.0
Total Current Liabilities	683.4	769.4
Long-term debt	3,405.7	3,206.9
Deferred income taxes	1,603.3	1,493.5
Asset retirement obligations	179.9	191.4
Fair value of derivative contracts	0	3.6
Other long-term liabilities	123.7	130.0
Commitments and contingencies
EQUITY
Common stock - par value $0.01 per share; 500.0 million shares authorized; 179.6 million and 178.5 million shares issued, respectively	1.8	1.8
Treasury stock - 0.3 million and 0.1 million shares, respectively	(12.6)	(3.7)
Additional paid-in capital	480.8	462.1
Retained earnings	2,940.0	2,773.0
Accumulated other comprehensive income	(5.4)	32.8
Total Common Shareholders' Equity	3,404.6	3,266.0
Noncontrolling interest	46.5	47.7
Total Equity	3,451.1	3,313.7
TOTAL LIABILITIES AND EQUITY	$ 9,447.1	$ 9,108.5