Supplemental Guarantor/Non-Guarantor Financial Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Unaudited Supplemental Condensed Consolidated Statements of Operations
Total revenues	$ 2,058.8	$ 1,980.6	$ 6,060.6	$ 5,666.1
Costs and expenses
Operating costs and expenses	1,509.0	1,399.4	4,396.8	3,958.7
Depreciation, depletion and amortization	172.5	108.4	470.7	317.6
Asset retirement obligation expenses	21.1	14.6	53.3	43.3
Selling and administrative expenses	68.7	71.2	202.4	191.4
Other operating (income) loss:
Net (gain) loss on disposal or exchange of assets	(0.2)	(1.7)	(7.6)	(31.4)
(Income) loss from equity affiliates	21.2	3.2	50.5	9.0
Interest expense	99.4	59.2	308.3	159.1
Interest income	(5.1)	(4.1)	(19.7)	(11.7)
Unrealized (gain) loss on derivatives	0		0
Income (loss) from continuing operations before income taxes	172.2	330.4	605.9	1,030.1
Income tax provision (benefit)	49.3	39.2	85.5	238.8
Income (loss) from continuing operations, net of income taxes	122.9	291.2	520.4	791.3
Loss from discontinued operations, net of income taxes	(81.3)	(9.7)	(92.7)	(38.9)
Net income (loss)	41.6	281.5	427.7	752.4
Less: Net (loss) income attributable to noncontrolling interests	(1.3)	7.4	7.4	17.0
Net income (loss) attributable to common stockholders	42.9	274.1	420.3	735.4
Comprehensive income (loss) attributable to common stockholders	119.3	82.4	585.9	664.2
Parent Company [Member]
Unaudited Supplemental Condensed Consolidated Statements of Operations
Total revenues	0	0	0	0
Costs and expenses
Operating costs and expenses	(95.6)	(99.3)	(313.2)	(289.3)
Depreciation, depletion and amortization	0	0	0	0
Asset retirement obligation expenses	0	0	0	0
Selling and administrative expenses	8.3	8.0	29.2	24.9
Other operating (income) loss:
Net (gain) loss on disposal or exchange of assets	0	0	0	0
(Income) loss from equity affiliates	(117.0)	(252.5)	(407.9)	(664.3)
Interest expense	101.8	61.0	312.1	162.3
Interest income	(72.9)	(4.1)	(224.3)	(12.8)
Unrealized (gain) loss on derivatives	0		0
Income (loss) from continuing operations before income taxes	175.4	286.9	604.1	779.2
Income tax provision (benefit)	131.8	12.9	182.7	43.1
Income (loss) from continuing operations, net of income taxes	43.6	274.0	421.4	736.1
Loss from discontinued operations, net of income taxes	(0.7)	0.1	(1.1)	(0.7)
Net income (loss)	42.9	274.1	420.3	735.4
Less: Net (loss) income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to common stockholders	42.9	274.1	420.3	735.4
Comprehensive income (loss) attributable to common stockholders	119.3	82.4	585.9	664.2
Guarantor Subsidiaries [Member]
Unaudited Supplemental Condensed Consolidated Statements of Operations
Total revenues	1,336.9	1,213.3	3,539.2	3,427.8
Costs and expenses
Operating costs and expenses	882.8	905.0	2,546.9	2,619.7
Depreciation, depletion and amortization	84.8	69.6	232.0	210.5
Asset retirement obligation expenses	11.8	11.0	34.7	30.7
Selling and administrative expenses	54.5	52.5	154.5	151.0
Other operating (income) loss:
Net (gain) loss on disposal or exchange of assets	(1.4)	(1.8)	(6.3)	(32.3)
(Income) loss from equity affiliates	1.9	2.7	5.7	6.4
Interest expense	5.8	13.7	12.9	40.6
Interest income	(46.8)	(5.2)	(112.6)	(15.8)
Unrealized (gain) loss on derivatives	(112.3)		(69.6)
Income (loss) from continuing operations before income taxes	455.8	165.8	741.0	417.0
Income tax provision (benefit)	101.7	46.7	155.3	109.0
Income (loss) from continuing operations, net of income taxes	354.1	119.1	585.7	308.0
Loss from discontinued operations, net of income taxes	(75.9)	(7.7)	(78.0)	(6.3)
Net income (loss)	278.2	111.4	507.7	301.7
Less: Net (loss) income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to common stockholders	278.2	111.4	507.7	301.7
Comprehensive income (loss) attributable to common stockholders	291.7	121.5	548.6	337.3
Non-Guarantor Subsidiaries [Member]
Unaudited Supplemental Condensed Consolidated Statements of Operations
Total revenues	778.3	811.3	2,694.4	2,456.5
Costs and expenses
Operating costs and expenses	778.2	637.7	2,336.1	1,846.5
Depreciation, depletion and amortization	87.7	38.8	238.7	107.1
Asset retirement obligation expenses	9.3	3.6	18.6	12.6
Selling and administrative expenses	5.9	10.7	18.7	15.5
Other operating (income) loss:
Net (gain) loss on disposal or exchange of assets	1.2	0.1	(1.3)	0.9
(Income) loss from equity affiliates	19.3	0.5	44.8	2.6
Interest expense	124.4	1.9	350.3	7.5
Interest income	(18.0)	(12.2)	(49.8)	(34.4)
Unrealized (gain) loss on derivatives	112.3		69.6
Income (loss) from continuing operations before income taxes	(342.0)	130.2	(331.3)	498.2
Income tax provision (benefit)	(184.2)	(20.4)	(252.5)	86.7
Income (loss) from continuing operations, net of income taxes	(157.8)	150.6	(78.8)	411.5
Loss from discontinued operations, net of income taxes	(4.7)	(2.1)	(13.6)	(31.9)
Net income (loss)	(162.5)	148.5	(92.4)	379.6
Less: Net (loss) income attributable to noncontrolling interests	(1.3)	7.4	7.4	17.0
Net income (loss) attributable to common stockholders	(161.2)	141.1	(99.8)	362.6
Comprehensive income (loss) attributable to common stockholders	(175.8)	205.2	34.4	405.8
Eliminations [Member]
Unaudited Supplemental Condensed Consolidated Statements of Operations
Total revenues	(56.4)	(44.0)	(173.0)	(218.2)
Costs and expenses
Operating costs and expenses	(56.4)	(44.0)	(173.0)	(218.2)
Depreciation, depletion and amortization	0	0	0	0
Asset retirement obligation expenses	0	0	0	0
Selling and administrative expenses	0	0	0	0
Other operating (income) loss:
Net (gain) loss on disposal or exchange of assets	0	0	0	0
(Income) loss from equity affiliates	117.0	252.5	407.9	664.3
Interest expense	(132.6)	(17.4)	(367.0)	(51.3)
Interest income	132.6	17.4	367.0	51.3
Unrealized (gain) loss on derivatives	0		0
Income (loss) from continuing operations before income taxes	(117.0)	(252.5)	(407.9)	(664.3)
Income tax provision (benefit)	0	0	0	0
Income (loss) from continuing operations, net of income taxes	(117.0)	(252.5)	(407.9)	(664.3)
Loss from discontinued operations, net of income taxes	0	0	0	0
Net income (loss)	(117.0)	(252.5)	(407.9)	(664.3)
Less: Net (loss) income attributable to noncontrolling interests	0	0	0	0
Net income (loss) attributable to common stockholders	(117.0)	(252.5)	(407.9)	(664.3)
Comprehensive income (loss) attributable to common stockholders	$ (115.9)	$ (326.7)	$ (583.0)	$ (743.1)
Senior Notes Due April 2016
Condensed Financial Statements, Captions [Line Items]
Interest rates on Senior Notes	5.875%		5.875%
7.375% Senior Notes due November 2016 [Member]
Condensed Financial Statements, Captions [Line Items]
Interest rates on Senior Notes	7.375%		7.375%
Senior Notes due September 2018
Condensed Financial Statements, Captions [Line Items]
Interest rates on Senior Notes	6.00%		6.00%
Senior Notes due September 2020
Condensed Financial Statements, Captions [Line Items]
Interest rates on Senior Notes	6.50%		6.50%
Senior Notes due September 2021
Condensed Financial Statements, Captions [Line Items]
Interest rates on Senior Notes	6.25%		6.25%
7.875% Senior Notes due November 2026 [Member]
Condensed Financial Statements, Captions [Line Items]
Interest rates on Senior Notes	7.875%		7.875%