Significant Accounting Policies (Gain on Asset Dispositions) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Disposition gains	$ 44.1	$ 49.7	$ 90.3
Residual sharing income	(10.2)	(83.6)	(13.4)
Non-remarketing disposition gains	(8.4)	(3.2)	(9.4)
Asset impairments	(8.6)	(38.5)	(33.9)
Net Gain on Asset Dispositions	$ 54.1	$ 98.0	$ 79.2

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Period Type:	duration