Held for Sale (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 19.8	$ (2.7)	$ 13.7	$ (12.8)
Asset Retirement Obligation, Held for Sale	117.2		117.2		$ 116.6
Subsidiaries [Member]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	$ 37.5	$ 20.0	$ 73.9	$ 60.1

Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Name:	us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration