Share-based Compensation Awards (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-settled awards
Stock-based Payment Award
Awards granted	0.8	1.1	0.8
Weighted-average grant-date fair value (per award)	$ 24.18	$ 21.87	$ 22.07
Total fair value of vested awards distributed	$ 22.6	$ 17.5	$ 18.8
Accrued dividends on non-vested stock-settled awards	1.5	1.3
Dividends paid for stock-settled awards	$ 1.2	$ 0.6
Cash-settled awards
Stock-based Payment Award
Awards granted	0.0	0.1	0.1
Weighted-average grant-date fair value (per award)	$ 23.33	$ 22.54	$ 20.46
Total fair value of vested awards distributed	$ 0.9	$ 0.7	$ 0.2
Performance-based awards
Stock-based Payment Award
Awards granted	4.8	3.3	2.9
Weighted-average grant-date fair value (per award)	$ 20.06	$ 19.58	$ 20.88
Total fair value of vested awards distributed	$ 112.4	$ 27.9	$ 18.7

Dividends paid for stock-settled awards vested during the period.

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- Definition

Stock based awards expected to be settled in cash

+ References

No definition available.

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- Definition

Amount of paid and unpaid stock dividends declared and applicable to holders of share-based compensation, for example, but not limited to, non-vested shares, stock options, or restricted stock units.

+ References

No definition available.

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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

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.

+ References

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=96867065&loc=d3e5070-113901

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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