Supplemental Guarantor/Non-Guarantor Financial Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Total revenues	$ 1,626.8	$ 1,748.0
Operating costs and expenses (exclusive of items shown separately below)	1,394.8	1,389.4
Depreciation, depletion and amortization	157.2	170.7
Asset retirement obligation expenses	15.6	19.0
Selling and administrative expenses	59.5	65.1
Other operating (income) loss:
Net gain on disposal or exchange of assets	(9.8)	(2.6)
(Income) loss from equity affiliates and investment in subsidiaries	6.6	17.6
Interest expense	103.3	101.3
Interest income	(3.6)	(5.9)
Unrealized (gain) loss on derivatives		0
(Loss) income from continuing operations before income taxes	(96.8)	(6.6)
Income tax (benefit) provision	(52.5)	3.7
(Loss) income from continuing operations, net of income taxes	(44.3)	(10.3)
Income (loss) from discontinued operations, net of income taxes	0.2	(9.1)
Net (loss) income	(44.1)	(19.4)
Less: Net income attributable to noncontrolling interests	4.4	4.0
Net (loss) income attributable to common stockholders	(48.5)	(23.4)
Other comprehensive income (loss), net of income taxes	125.9	0.6
Comprehensive income (loss)	81.8	(18.8)
Less: Comprehensive income attributable to noncontrolling interests	4.4	4.0
Comprehensive income (loss) attributable to common stockholders	77.4	(22.8)
Parent Company [Member]
Total revenues	0	0
Operating costs and expenses (exclusive of items shown separately below)	21.2	(91.7)
Depreciation, depletion and amortization	0	0
Asset retirement obligation expenses	0	0
Selling and administrative expenses	13.6	9.2
Other operating (income) loss:
Net gain on disposal or exchange of assets	0	0
(Income) loss from equity affiliates and investment in subsidiaries	(39.6)	84.8
Interest expense	105.7	101.9
Interest income	(0.1)	(68.1)
Unrealized (gain) loss on derivatives		0
(Loss) income from continuing operations before income taxes	(100.8)	(36.1)
Income tax (benefit) provision	(52.0)	(15.3)
(Loss) income from continuing operations, net of income taxes	(48.8)	(20.8)
Income (loss) from discontinued operations, net of income taxes	0.3	(2.6)
Net (loss) income	(48.5)	(23.4)
Less: Net income attributable to noncontrolling interests	0	0
Net (loss) income attributable to common stockholders	(48.5)	(23.4)
Other comprehensive income (loss), net of income taxes	125.9	0.6
Comprehensive income (loss)	77.4	(22.8)
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to common stockholders	77.4	(22.8)
Guarantor Subsidiaries [Member]
Total revenues	976.4	1,014.6
Operating costs and expenses (exclusive of items shown separately below)	726.8	700.9
Depreciation, depletion and amortization	77.2	79.6
Asset retirement obligation expenses	8.6	11.6
Selling and administrative expenses	41.3	47.4
Other operating (income) loss:
Net gain on disposal or exchange of assets	(9.6)	(2.8)
(Income) loss from equity affiliates and investment in subsidiaries	0.6	3.9
Interest expense	1.6	2.3
Interest income	(2.4)	(34.9)
Unrealized (gain) loss on derivatives		(41.0)
(Loss) income from continuing operations before income taxes	132.3	247.6
Income tax (benefit) provision	24.8	107.9
(Loss) income from continuing operations, net of income taxes	107.5	139.7
Income (loss) from discontinued operations, net of income taxes	(0.7)	(1.5)
Net (loss) income	106.8	138.2
Less: Net income attributable to noncontrolling interests	0	0
Net (loss) income attributable to common stockholders	106.8	138.2
Other comprehensive income (loss), net of income taxes	9.9	(22.5)
Comprehensive income (loss)	116.7	115.7
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to common stockholders	116.7	115.7
Non-Guarantor Subsidiaries [Member]
Total revenues	671.3	796.2
Operating costs and expenses (exclusive of items shown separately below)	667.7	843.0
Depreciation, depletion and amortization	80.0	91.1
Asset retirement obligation expenses	7.0	7.4
Selling and administrative expenses	4.6	8.5
Other operating (income) loss:
Net gain on disposal or exchange of assets	(0.2)	0.2
(Income) loss from equity affiliates and investment in subsidiaries	6.0	13.7
Interest expense	1.4	110.5
Interest income	(6.5)	(16.3)
Unrealized (gain) loss on derivatives		41.0
(Loss) income from continuing operations before income taxes	(88.7)	(302.9)
Income tax (benefit) provision	(25.3)	(88.9)
(Loss) income from continuing operations, net of income taxes	(63.4)	(214.0)
Income (loss) from discontinued operations, net of income taxes	0.6	(5.0)
Net (loss) income	(62.8)	(219.0)
Less: Net income attributable to noncontrolling interests	4.4	4.0
Net (loss) income attributable to common stockholders	(67.2)	(223.0)
Other comprehensive income (loss), net of income taxes	(18.5)	(14.2)
Comprehensive income (loss)	(81.3)	(233.2)
Less: Comprehensive income attributable to noncontrolling interests	4.4	4.0
Comprehensive income (loss) attributable to common stockholders	(85.7)	(237.2)
Eliminations [Member]
Total revenues	(20.9)	(62.8)
Operating costs and expenses (exclusive of items shown separately below)	(20.9)	(62.8)
Depreciation, depletion and amortization	0	0
Asset retirement obligation expenses	0	0
Selling and administrative expenses	0	0
Other operating (income) loss:
Net gain on disposal or exchange of assets	0	0
(Income) loss from equity affiliates and investment in subsidiaries	39.6	(84.8)
Interest expense	(5.4)	(113.4)
Interest income	5.4	113.4
Unrealized (gain) loss on derivatives		0
(Loss) income from continuing operations before income taxes	(39.6)	84.8
Income tax (benefit) provision	0	0
(Loss) income from continuing operations, net of income taxes	(39.6)	84.8
Income (loss) from discontinued operations, net of income taxes	0	0
Net (loss) income	(39.6)	84.8
Less: Net income attributable to noncontrolling interests	0	0
Net (loss) income attributable to common stockholders	(39.6)	84.8
Other comprehensive income (loss), net of income taxes	8.6	36.7
Comprehensive income (loss)	(31.0)	121.5
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income (loss) attributable to common stockholders	$ (31.0)	$ 121.5