Share-Based Compensation (Share-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share based compensation expense	$ 22.5	$ 19.1	$ 53.3	$ 43.9
Tax benefit	(5.5)	(7.3)	(13.0)	(16.8)
After-tax expense	17.0	11.8	40.3	27.1
Stock Options [Member]
Share based compensation expense	5.7	4.0	18.0	12.7
Restricted Stock Units (RSUs) [Member]
Share based compensation expense	8.7	6.6	22.0	16.9
Performance Shares [Member]
Share based compensation expense	6.9	6.8	11.3	11.2
Other share based compensation [Member]
Share based compensation expense	$ 1.2	$ 1.7	$ 2.0	$ 3.1

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=96867065&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=96867065&loc=d3e5070-113901

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