Non-vested Award Activity (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
Non-vested as of January 1, 2017	2.3
Nonvested as of January 1, 2017, weighted-average grant date fair value	$ 20.84
Granted	0.8
Granted, Weighted-average grant-date fair value	$ 24.18	$ 21.87	$ 22.07
Vested	(1.0)
Vested, Weighted-average grant date fair value	$ 19.49
Forfeited	0.0
Forfeited, Weighted-average grant date fair value	$ 21.86
Non-vested as of December 31, 2017	2.1	2.3
Nonvested as of December 31, 2017, weighted-average grant date fair value	$ 22.78	$ 20.84
Total unrecognized compensation expense remaining	$ 24.1
Weighted-average years expected to be recognized over	1 year
Cash-settled awards
Stock-based Payment Award
Non-vested as of January 1, 2017	0.1
Nonvested as of January 1, 2017, weighted-average grant date fair value	$ 20.49
Granted	0.0
Granted, Weighted-average grant-date fair value	$ 23.33	$ 22.54	$ 20.46
Vested	0.0
Vested, Weighted-average grant date fair value	$ 19.27
Forfeited	0.0
Forfeited, Weighted-average grant date fair value	$ 20.50
Non-vested as of December 31, 2017	0.1	0.1
Nonvested as of December 31, 2017, weighted-average grant date fair value	$ 22.52	$ 20.49
Total unrecognized compensation expense remaining	$ 1.0
Weighted-average years expected to be recognized over	1 year
Cash awards granted during the period target value	$ 2.8	$ 5.2	$ 1.3
Incentive compensation expense, non share-based	$ 2.5	$ 3.1	$ 3.0
Performance-based awards
Stock-based Payment Award
Non-vested as of January 1, 2017	8.5
Nonvested as of January 1, 2017, weighted-average grant date fair value	$ 19.16
Granted	4.8
Granted, Weighted-average grant-date fair value	$ 20.06	$ 19.58	$ 20.88
Vested	(4.6)
Vested, Weighted-average grant date fair value	$ 16.64
Forfeited	(0.4)
Forfeited, Weighted-average grant date fair value	$ 20.00
Non-vested as of December 31, 2017	8.3	8.5
Nonvested as of December 31, 2017, weighted-average grant date fair value	$ 21.05	$ 19.16
Total unrecognized compensation expense remaining	$ 71.9
Weighted-average years expected to be recognized over	1 year 8 months
Cash awards granted during the period target value	$ 38.4	$ 37.4	$ 31.8
Incentive compensation expense, non share-based	$ 35.3	$ 39.8	$ 35.8

Target value of all cash awards granted during the period (settled in shares or cash)

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- Definition

Represents the expense recognized during the period arising from cash-based incentive compensation arrangements with employees, directors and certain consultants qualifying for treatment as employees.

+ References

No definition available.

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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.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ 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)(1)(iv)(3)
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

+ 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)(3)
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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
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-SubTopic 10
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-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
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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
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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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

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- Definition

The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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.

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