Supplemental Guarantor/Non-Guarantor Financial Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Total revenues	$ 1,797.6	$ 2,058.8	$ 5,270.9	$ 6,060.6
Operating costs and expenses (exclusive of items shown separately below)	1,432.1	1,501.3	4,258.7	4,389.1
Depreciation, depletion and amortization	186.4	172.5	542.8	470.7
Asset retirement obligation expenses	13.4	21.1	50.7	53.3
Selling and administrative expenses	55.0	68.7	184.1	202.4
Net gain on disposal or exchange of assets	(4.1)	(0.2)	(49.9)	(7.6)
Asset impairment	0	7.7	21.5	7.7
(Income) loss from equity affiliates and investment in subsidiaries	2.6	21.2	35.6	50.5
Interest expense	111.0	99.4	323.1	308.3
Interest income	(4.2)	(5.1)	(11.2)	(19.7)
Unrealized (gain) loss on derivatives	0	0	0	0
(Loss) income from continuing operations before income taxes	5.4	172.2	(84.5)	605.9
Income tax provision (benefit)	(18.6)	49.3	(199.6)	85.5
(Loss) income from continuing operations, net of income taxes	24.0	122.9	115.1	520.4
Loss from discontinued operations, net of income taxes	(43.1)	(81.3)	(66.5)	(92.7)
Net (loss) income	(19.1)	41.6	48.6	427.7
Less: Net income (loss) attributable to noncontrolling interests	7.0	(1.3)	7.8	7.4
Net (loss) income attributable to common stockholders	(26.1)	42.9	40.8	420.3
Other comprehensive income (loss), net of income taxes	14.1	76.4	(416.9)	165.6
Comprehensive (loss) income	(5.0)	118.0	(368.3)	593.3
Comprehensive (loss) income attributable to common stockholders	(12.0)	119.3	(376.1)	585.9
Parent Company [Member]
Total revenues	0	0	0	0
Operating costs and expenses (exclusive of items shown separately below)	(14.4)	(95.6)	(168.9)	(313.2)
Depreciation, depletion and amortization	0	0	0	0
Asset retirement obligation expenses	0	0	0	0
Selling and administrative expenses	11.2	8.3	39.5	29.2
Net gain on disposal or exchange of assets	0	0	0	0
Asset impairment		0	21.5	0
(Income) loss from equity affiliates and investment in subsidiaries	(98.0)	(117.0)	(192.1)	(407.9)
Interest expense	113.0	101.8	316.2	312.1
Interest income	(0.1)	(72.9)	(68.3)	(224.3)
Unrealized (gain) loss on derivatives	0	0	0	0
(Loss) income from continuing operations before income taxes	(11.7)	175.4	52.1	604.1
Income tax provision (benefit)	10.0	131.8	0.5	182.7
(Loss) income from continuing operations, net of income taxes	(21.7)	43.6	51.6	421.4
Loss from discontinued operations, net of income taxes	(4.4)	(0.7)	(10.8)	(1.1)
Net (loss) income	(26.1)	42.9	40.8	420.3
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net (loss) income attributable to common stockholders	(26.1)	42.9	40.8	420.3
Other comprehensive income (loss), net of income taxes	14.1	76.4	(416.9)	165.6
Comprehensive (loss) income	(12.0)	119.3	(376.1)	585.9
Comprehensive (loss) income attributable to common stockholders	(12.0)	119.3	(376.1)	585.9
Guarantor Subsidiaries [Member]
Total revenues	1,005.8	1,336.9	2,992.9	3,539.2
Operating costs and expenses (exclusive of items shown separately below)	755.6	875.1	2,279.5	2,539.2
Depreciation, depletion and amortization	83.0	84.8	248.1	232.0
Asset retirement obligation expenses	4.8	11.8	26.6	34.7
Selling and administrative expenses	38.5	54.5	125.7	154.5
Net gain on disposal or exchange of assets	(4.0)	(1.4)	(49.8)	(6.3)
Asset impairment		7.7	0	7.7
(Income) loss from equity affiliates and investment in subsidiaries	2.0	1.9	10.4	5.7
Interest expense	88.2	5.8	99.2	12.9
Interest income	(98.8)	(46.8)	(138.5)	(112.6)
Unrealized (gain) loss on derivatives	(19.7)	(112.3)	441.9	(69.6)
(Loss) income from continuing operations before income taxes	156.2	455.8	(50.2)	741.0
Income tax provision (benefit)	(32.2)	101.7	(117.4)	155.3
(Loss) income from continuing operations, net of income taxes	188.4	354.1	67.2	585.7
Loss from discontinued operations, net of income taxes	(1.8)	(75.9)	(4.3)	(78.0)
Net (loss) income	186.6	278.2	62.9	507.7
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net (loss) income attributable to common stockholders	186.6	278.2	62.9	507.7
Other comprehensive income (loss), net of income taxes	14.2	13.5	42.7	40.9
Comprehensive (loss) income	200.8	291.7	105.6	548.6
Comprehensive (loss) income attributable to common stockholders	200.8	291.7	105.6	548.6
Non-Guarantor Subsidiaries [Member]
Total revenues	823.8	778.3	2,438.8	2,694.4
Operating costs and expenses (exclusive of items shown separately below)	722.9	778.2	2,308.9	2,336.1
Depreciation, depletion and amortization	103.4	87.7	294.7	238.7
Asset retirement obligation expenses	8.6	9.3	24.1	18.6
Selling and administrative expenses	5.3	5.9	18.9	18.7
Net gain on disposal or exchange of assets	(0.1)	1.2	(0.1)	(1.3)
Asset impairment		0	0	0
(Income) loss from equity affiliates and investment in subsidiaries	0.6	19.3	25.2	44.8
Interest expense	22.6	124.4	142.8	350.3
Interest income	(18.1)	(18.0)	(39.5)	(49.8)
Unrealized (gain) loss on derivatives	19.7	112.3	(441.9)	69.6
(Loss) income from continuing operations before income taxes	(41.1)	(342.0)	105.7	(331.3)
Income tax provision (benefit)	3.6	(184.2)	(82.7)	(252.5)
(Loss) income from continuing operations, net of income taxes	(44.7)	(157.8)	188.4	(78.8)
Loss from discontinued operations, net of income taxes	(36.9)	(4.7)	(51.4)	(13.6)
Net (loss) income	(81.6)	(162.5)	137.0	(92.4)
Less: Net income (loss) attributable to noncontrolling interests	7.0	(1.3)	7.8	7.4
Net (loss) income attributable to common stockholders	(88.6)	(161.2)	129.2	(99.8)
Other comprehensive income (loss), net of income taxes	(36.4)	(14.6)	(100.5)	134.2
Comprehensive (loss) income	(118.0)	(177.1)	36.5	41.8
Comprehensive (loss) income attributable to common stockholders	(125.0)	(175.8)	28.7	34.4
Consolidation, Eliminations [Member]
Total revenues	(32.0)	(56.4)	(160.8)	(173.0)
Operating costs and expenses (exclusive of items shown separately below)	(32.0)	(56.4)	(160.8)	(173.0)
Depreciation, depletion and amortization	0	0	0	0
Asset retirement obligation expenses	0	0	0	0
Selling and administrative expenses	0	0	0	0
Net gain on disposal or exchange of assets	0	0	0	0
Asset impairment		0	0	0
(Income) loss from equity affiliates and investment in subsidiaries	98.0	117.0	192.1	407.9
Interest expense	(112.8)	(132.6)	(235.1)	(367.0)
Interest income	112.8	132.6	235.1	367.0
Unrealized (gain) loss on derivatives	0	0	0	0
(Loss) income from continuing operations before income taxes	(98.0)	(117.0)	(192.1)	(407.9)
Income tax provision (benefit)	0	0	0	0
(Loss) income from continuing operations, net of income taxes	(98.0)	(117.0)	(192.1)	(407.9)
Loss from discontinued operations, net of income taxes	0	0	0	0
Net (loss) income	(98.0)	(117.0)	(192.1)	(407.9)
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0
Net (loss) income attributable to common stockholders	(98.0)	(117.0)	(192.1)	(407.9)
Other comprehensive income (loss), net of income taxes	22.2	1.1	57.8	(175.1)
Comprehensive (loss) income	(75.8)	(115.9)	(134.3)	(583.0)
Comprehensive (loss) income attributable to common stockholders	$ (75.8)	$ (115.9)	$ (134.3)	$ (583.0)