Divestitures - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								9 Months Ended	12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2016	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Nov. 08, 2015	Feb. 14, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 45.8	$ (234.5)	$ (40.6)	$ 5.0	$ (32.1)	$ (16.7)	$ (152.4)	$ (20.3)		$ (224.3)	$ (221.5)	$ 87.3
Net (loss) income	36.2	(93.0)	$ 15.9	$ 7.0	(127.1)	$ (41.4)	$ (237.5)	$ (106.4)		(33.9)	(512.4)	101.7
Deferred Tax Assets, Valuation Allowance	512.1				894.2					512.1	894.2
Compass Production Partners G.P. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (loss) income										40.8	(368.6)	(67.7)
Gain (Loss) on Disposition of Oil and Gas Property										105.6	0.0	0.0
FGL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities, Current	9.9				0.0					9.9	0.0
Disposal Group, Including Discontinued Operation, Write-down of assets held for sale to fair value less costs to sell	(362.8)				0.0					(362.8)	0.0
Discontinued Operation, Tax Effect of Discontinued Operation, Deferred Taxes, Current									$ 15.2
Deferred Tax Liabilities, Parent's Basis in Discontinued Operation		367.9							367.9
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest										(265.1)	147.1	155.0
Deferred Tax Assets, Valuation Allowance		$ 94.7							$ 94.7
Business Acquisition, Termination Fee Payable for Termination of Merger Agreement	$ 51.5									51.5
Majority-Owned Subsidiary, Unconsolidated [Member] | FGL [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Disposal Group, Including Discontinued Operation, Interest Income										$ 4.1	4.5	4.5
Compass Production Partners G.P. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired	100.00%									100.00%
HGI Energy Holdings, LLC | Compass
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired														73.50%
EXCO [Member] | Compass
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired														24.50%
EXCO/HGI General Partner | Compass
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired														2.00%
HGI
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net (loss) income										$ (198.8)	(556.8)	$ (10.3)
Deferred Tax Assets, Valuation Allowance	$ 266.4				$ 594.5					$ 266.4	$ 594.5
HGI | Compass
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition Percentage Of Equity Interests Acquired	74.40%									74.40%
Compass Production Partners [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Combination, Consideration Transferred										$ 118.8
FGL [Member] | Anbang Insurance Group Co., Ltd. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Business Acquisition, Share Price													$ 26.80