CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current Assets
Cash and cash equivalents	$ 123.0	$ 0
Accounts receivable, net	321.9	387.5
Fair value of derivative contracts	39.4	188.7
Gas, oil and NGL inventories at lower of average cost or market	13.1	13.1
Prepaid expenses and other	49.4	68.0
Deferred income taxes	0	0
Total Current Assets	546.8	657.3
Property, Plant and Equipment (successful efforts method for gas and oil properties)
Proved properties	11,038.8	10,234.3
Unproved properties	911.8	937.9
Midstream field services	1,670.4	1,634.9
Marketing and other	80.4	64.6
Material and supplies	63.4	61.9
Total Property, Plant and Equipment	13,764.8	12,933.6
Less Accumulated Depreciation, Depletion and Amortization
Exploration and production	4,747.4	4,258.1
Midstream field services	394.7	357.9
Marketing and other	20.3	18.1
Total Accumulated Depreciation, Depletion and Amortization	5,162.4	4,634.1
Net Property, Plant and Equipment	8,602.4	8,299.5
Investment in unconsolidated affiliates	39.0	41.2
Goodwill	59.5	59.5
Fair value of derivative contracts	5.8	4.1
Other noncurrent assets	53.2	46.9
TOTAL ASSETS	9,306.7	9,108.5
Current Liabilities
Checks outstanding in excess of cash balances	1.6	39.7
Accounts payable and accrued expenses	593.6	643.4
Production and property taxes	58.0	41.8
Interest payable	34.6	36.9
Fair value of derivative contracts	10.1	2.6
Deferred income taxes	9.5	5.0
Total Current Liabilities	707.4	769.4
Long-term debt	2,882.3	3,206.9
Deferred income taxes	1,494.7	1,493.5
Asset retirement obligations	168.4	191.4
Fair value of derivative contracts	0	3.6
Other long-term liabilities	129.0	130.0
Commitments and contingencies
EQUITY
Common stock - par value $0.01 per share; 500.0 million shares authorized; 179.3 million and 178.5 million shares issued, respectively	1.8	1.8
Treasury stock - 0.4 million and 0.1 million shares, respectively	(14.7)	(3.7)
Additional paid-in capital	489.3	462.1
Retained earnings	2,973.7	2,773.0
Accumulated other comprehensive income	(24.0)	32.8
Total Common Shareholders' Equity	3,426.1	3,266.0
Noncontrolling interest	498.8	47.7
Total Equity	3,924.9	3,313.7
TOTAL LIABILITIES AND EQUITY	$ 9,306.7	$ 9,108.5