Supplemental Guarantor/Non-Guarantor Financial Information (Details 4) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Revenues	$ 1,040.2	$ 916.8	$ 1,339.3	$ 2,067.4	$ 2,877.2
Operating Costs and Expenses	996.2	844.7	1,198.8	1,916.4	2,520.4
Depreciation, Depletion and Amortization	115.9	99.0	147.1	227.7	294.6
Asset Retirement Obligation, Accretion Expense	11.5	9.7	13.9	24.6	28.1
Selling, General and Administrative Expense	34.2	19.8	41.6	82.5	91.0
Restructuring charges	3.1	2.5	21.2	15.2	21.2
Gain (Loss) on Disposition of Assets	(13.7)	(13.7)	(12.2)	(15.5)	(12.3)
Loss (income) from equity affiliates and investment in subsidiaries	0.7	(0.3)	3.9	9.7	7.0
Interest expense	59.0	37.0	118.9	185.2	225.5
Interest income	(1.3)	(1.0)	(2.7)	(2.7)	(5.2)
Reorganization Items	(95.4)	95.4	0.0	(95.4)	0.0
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	(260.8)	(176.3)	(1,100.3)	(488.3)	(1,261.7)
Income Tax Expense (Benefit)	(30.0)	(18.0)	(93.1)	(95.8)	(90.1)
Loss from continuing operations, net of income taxes	(230.8)	(158.3)	(1,007.2)	(392.5)	(1,171.6)
(Loss) income from discontinued operations, net of income taxes	(3.0)	(2.4)	(36.3)	(6.4)	(45.2)
Net loss	(233.8)	(160.7)	(1,043.5)	(398.9)	(1,216.8)
Less: Net income attributable to noncontrolling interests	1.7	1.7	1.8	1.7	5.1
Net (loss) income attributable to common stockholders	(235.5)	(162.4)	(1,045.3)	(400.6)	(1,221.9)
Asset impairment	0.0		900.8	17.2	900.8
Debtor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues		538.2
Operating Costs and Expenses		437.5
Depreciation, Depletion and Amortization		49.7
Asset Retirement Obligation, Accretion Expense		5.2
Selling, General and Administrative Expense		19.5
Restructuring charges		2.0
Gain (Loss) on Disposition of Assets		(10.9)
Loss (income) from equity affiliates and investment in subsidiaries		91.8
Interest expense		33.8
Interest income		(0.9)
Reorganization Items		93.0
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest		(182.5)
Income Tax Expense (Benefit)		(22.5)
Loss from continuing operations, net of income taxes		(160.0)
(Loss) income from discontinued operations, net of income taxes		(2.4)
Net loss		(162.4)
Less: Net income attributable to noncontrolling interests		0.0
Net (loss) income attributable to common stockholders		(162.4)
Non-Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues	483.5		619.0	924.6	1,310.7
Operating Costs and Expenses	521.4		538.9	979.2	1,141.9
Depreciation, Depletion and Amortization	65.3		87.8	126.0	167.4
Asset Retirement Obligation, Accretion Expense	6.1		9.5	12.7	18.4
Selling, General and Administrative Expense	1.3		3.9	5.0	6.5
Restructuring charges	2.7		14.9	3.4	14.9
Gain (Loss) on Disposition of Assets	(2.8)		(0.5)	(2.8)	0.4
Loss (income) from equity affiliates and investment in subsidiaries	(0.2)		2.3	7.6	4.1
Interest expense	6.6		2.9	12.8	5.5
Interest income	(8.1)		(10.0)	(16.9)	(20.5)
Reorganization Items	(2.4)			(2.4)
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	(111.2)		(749.3)	(222.0)	(746.5)
Income Tax Expense (Benefit)	13.2		(3.0)	(1.0)	(0.1)
Loss from continuing operations, net of income taxes	(124.4)		(746.3)	(221.0)	(746.4)
(Loss) income from discontinued operations, net of income taxes	(0.1)		(0.6)	(1.0)	(8.7)
Net loss	(124.5)		(746.9)	(222.0)	(755.1)
Less: Net income attributable to noncontrolling interests	1.7		1.9	1.7	4.4
Net (loss) income attributable to common stockholders	(126.2)		(748.8)	(223.7)	(759.5)
Asset impairment			718.6	17.2
Non-Debtor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues		379.8
Operating Costs and Expenses		408.4
Depreciation, Depletion and Amortization		49.3
Asset Retirement Obligation, Accretion Expense		4.5
Selling, General and Administrative Expense		0.3
Restructuring charges		0.5
Gain (Loss) on Disposition of Assets		(2.8)
Loss (income) from equity affiliates and investment in subsidiaries		(1.1)
Interest expense		5.5
Interest income		(2.4)
Reorganization Items		2.4
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest		(84.8)
Income Tax Expense (Benefit)		4.5
Loss from continuing operations, net of income taxes		(89.3)
(Loss) income from discontinued operations, net of income taxes		0.0
Net loss		(89.3)
Less: Net income attributable to noncontrolling interests		1.7
Net (loss) income attributable to common stockholders		(91.0)
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Revenues	(65.9)	(1.2)	(106.0)	(143.7)	(230.8)
Operating Costs and Expenses	(65.9)	(1.2)	(106.0)	(143.7)	(230.8)
Depreciation, Depletion and Amortization	0.0	0.0	0.0	0.0	0.0
Asset Retirement Obligation, Accretion Expense	0.0	0.0	0.0	0.0	0.0
Selling, General and Administrative Expense	0.0	0.0	0.0	0.0	0.0
Restructuring charges	0.0	0.0	0.0	0.0	0.0
Gain (Loss) on Disposition of Assets	0.0	0.0	0.0	0.0	0.0
Loss (income) from equity affiliates and investment in subsidiaries	(37.1)	(91.0)	(800.0)	(90.4)	(695.6)
Interest expense	(8.0)	(2.3)	(8.3)	(16.4)	(17.0)
Interest income	8.0	2.3	8.3	16.4	17.0
Reorganization Items	0.0	0.0		0.0
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	37.1	91.0	800.0	90.4	695.6
Income Tax Expense (Benefit)	0.0	0.0	0.0	0.0	0.0
Loss from continuing operations, net of income taxes	37.1	91.0	800.0	90.4	695.6
(Loss) income from discontinued operations, net of income taxes	0.0	0.0	0.0	0.0	0.0
Net loss	37.1	91.0	800.0	90.4	695.6
Less: Net income attributable to noncontrolling interests	0.0	0.0	0.0	0.0	0.0
Net (loss) income attributable to common stockholders	$ 37.1	$ 91.0	800.0	90.4	$ 695.6
Asset impairment			$ 0.0	$ 0.0