Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations, net of income taxes	$ (4.1)		$ (3.4)
Other current assets	0.2	$ 0.2
Investments and other assets	15.9	15.9
Total assets classified as discontinued operations	16.1	16.1
Accounts payable and accrued expenses	50.6	55.9
Other noncurrent liabilities	199.7	198.5
Liabilities subject to compromise	8,416.7	8,440.2
Total liabilities classified as discontinued operations	271.2	275.3
Accounts Payable [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Liabilities subject to compromise	20.9	20.9
United Mine Workers of America [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations, net of income taxes	$ 56.0	$ 54.3