Share-Based Compensation (Share-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share based compensation expense	$ 4.4	$ 5.0	$ 15.1	$ 14.2
Tax benefit	(1.5)	(1.5)	(5.0)	(4.2)
After-tax expense	2.9	3.5	10.1	10.0
Stock Options [Member]
Share based compensation expense	0.7	1.1	2.7	3.3
Restricted Stock Units (RSUs) [Member]
Share based compensation expense	1.7	2.0	5.9	6.1
Performance Shares [Member]
Share based compensation expense	1.4	1.2	4.5	3.7
Deferred Compensation [Member]
Share based compensation expense	$ 0.6	$ 0.7	$ 2.0	$ 1.1

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration