Stock-Based Compensation Plans - Performance Share Awards and Restricted Stock Units (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($) $ / shares shares
Performance Share Awards
Change in nonvested units outstanding
Awards or units granted (in shares) \| shares	0.2
Awards or units granted weighted-average grant-date fair value (in dollars per share) \| $ / shares	$ 62.98
Other award and unit disclosures
Lower limit multiple of initial target awards (as a percent)	0.00%
Upper limit multiple of initial target awards (as a percent)	150.00%
Unrecognized compensation costs \| $	$ 7.0
Weighted-average service period over which unrecognized compensation costs will be recognized	1 year 1 month 6 days
Restricted Stock Units
Change in nonvested units outstanding
Awards or units granted (in shares) \| shares	0.8
Awards or units granted weighted-average grant-date fair value (in dollars per share) \| $ / shares	$ 62.81
Other award and unit disclosures
Unrecognized compensation costs \| $	$ 55.2
Weighted-average service period over which unrecognized compensation costs will be recognized	1 year 9 months 18 days

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- Definition

The lower limit multiple of initial target awards which will be used to determine the actual number of shares to be awarded at the end of each performance period for performance-based awards.

+ References

No definition available.

+ Details

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- Definition

The upper limit multiple of initial target awards which will be used to determine the actual number of shares to be awarded at the end of each performance period for performance-based awards.

+ References

No definition available.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ 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 (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

The number of grants made 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

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

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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