Stock-based Compensation (Details 3) (Performance Shares [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares or units distributed	$ 19.6	$ 9.9	$ 6.0
Realized tax benefits from tax deductions	$ 7.5	$ 3.8	$ 2.3

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)(2)

-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