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Shareholders' Equity - RSU Awards and SSAR Awards (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
RSUs |  |  |  |
Awards Outstanding |  |  |  |
Balance at the beginning of the period (in shares) | 1.2 | 0.7 | 0.8 |
Granted (in shares) | 0.6 | 0.7 | 0.3 |
Vested (in shares) | (0.2) | (0.1) | (0.3) |
Forfeited (in shares) | (0.1) | (0.1) | 0.0 |
Balance at the end of the period (in shares) | 1.6 | 1.2 | 0.7 | 0.8
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |  |  |  |
Balance at the beginning of the period (in dollars per share) | $ 43.28 | $ 43.10 | $ 38.55 |
Granted (in dollars per share) | 37.74 | 44.23 | 51.00 |
Vested (in dollars per share) | 43.06 | 42.78 | 38.80 |
Forfeited (in dollars per share) | 42.43 | 44.78 | 42.65 |
Balance at the end of the period (in dollars per share) | $ 41.01 | $ 43.28 | $ 43.10 | $ 38.55
Aggregate Intrinsic Value | $ 43.9 | $ 55.7 | $ 28.0 | $ 36.9
Weighted Average Remaining Vesting Term | 1 year 4 months 24 days | 1 year 7 months 6 days | 1 year 8 months 12 days | 1 year 6 months
Aggregate intrinsic value of awards issued | $ 7.7 | $ 6.2 | $ 15.3 |
SSAR Awards |  |  |  |
Awards Outstanding |  |  |  |
Balance at the beginning of the period (in shares) | 0.3 | 0.2 | 0.2 |
Granted (in shares) | 0.4 | 0.1 | 0.0 |
Exercised (in shares) | 0.0 | 0.0 | 0.0 |
Balance at the end of the period (in shares) | 0.7 | 0.3 | 0.2 | 0.2
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |  |  |  |
Balance at the beginning of the period (in dollars per share) | $ 44.97 | $ 42.91 | $ 40.06 |
Granted (in dollars per share) | 36.31 | 48.58 | 57.48 |
Exercised (in dollars per share) | 40.91 | 40.91 | 25.08 |
Balance at the end of the period (in dollars per share) | $ 40.27 | $ 44.97 | $ 42.91 | $ 40.06
Aggregate Intrinsic Value | $ 0.0 | $ 0.3 | $ 0.0 | $ 1.6
Weighted Average Remaining Vesting Term | 3 years | 2 years 4 months 24 days | 2 years 6 months | 3 years
SSAR Awards Exercisable |  |  |  |
SSAR Awards (in shares) | 0.2 | 0.2 | 0.1 | 0.1
Weighted Average Exercise Price (in dollars per share) | $ 42.76 | $ 42.15 | $ 42.06 | $ 35.81
Aggregate Intrinsic Value | $ 0.0 | $ 0.7 | $ 0.0 | $ 0.6
Weighted Average Remaining Contractual Life | 12 days | 1 year 3 months 18 days | 2 years 2 months 12 days | 2 years 2 months 12 days
Aggregate intrinsic value of SSAR Awards exercised |  | $ 0.1 | $ 0.5 |
Assumptions used to determine weighted average fair value |  |  |  |
Weighted average fair value of SSAR Awards (in dollars per share) | $ 8.82 | $ 12.32 | $ 14.78 |
Expected term | 4 years 3 months 18 days | 4 years 6 months | 4 years 3 months 18 days |
Volatility | 28.60% | 29.80% | 30.20% |
Dividend yields | 0.70% | 0.50% | 0.30% |
Risk-free interest rates | 1.80% | 1.20% | 1.20% |

X
- Definition The aggregate intrinsic value of outstanding awards of equity-based plans excluding option plans 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, as calculated by applying the disclosed pricing methodology. + References No definition available. + Details
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- Definition The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of equity-based payment instruments, excluding stock (or unit) options, outstanding and currently exercisable under the plan as of the balance sheet date. + References No definition available. + Details
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- Definition The number of shares into which fully or partially vested equity-based payment instruments, excluding stock (or unit) options, outstanding as of the balance sheet date that can be currently converted under the plan. + References No definition available. + Details
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- Definition The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of equity-based payment instruments, excluding stock (or unit) options, outstanding and currently exercisable under the plan. + References No definition available. + Details
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- Definition The weighted average period between the balance sheet date and expiration for all vested portions of equity-based payment instruments, excluding stock (or unit) options, outstanding and currently exercisable (or convertible) under the plan, which may be expressed in a decimal value. + References No definition available. + Details
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- Definition The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on equity-based payment instruments, excluding stock (or unit) options, which were exercised (or share units converted) into shares during the reporting period under the plan. + References No definition available. + Details
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- Definition The weighted average price at which equity-based payment instruments, excluding stock (or unit) options, are exercised during the reporting period. + References No definition available. + Details
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- Definition The weighted average price of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect during the reporting period as a result of the occurrence of a terminating event specified in the contractual agreement of the plan. + References No definition available. + Details
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- Definition The weighted average price at which equity-based payment instruments, excluding stock (or unit) options, are issued during the period on other than stock (or unit) option plans. + References No definition available. + Details
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- Definition The aggregate intrinsic value of awards issued of equity-based plans excluding option plans 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, as calculated by applying the disclosed pricing methodology. + References No definition available. + Details
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- Definition Weighted average price of nonvested awards on equity-based plans excluding option plans at which grantees can acquire the award under the plan. + References No definition available. + Details
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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) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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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 + Details
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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 + Details
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- Definition Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (e)(1) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The number of equity-based payment instruments, excluding stock (or unit) options, that vested 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)(2)(iii)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition 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. + 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)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term. + 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 (f)(2)(iii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the 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 (f)(2)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition The risk-free interest rate assumption that is used in valuing an option on its own shares. + 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 (f)(2)(iv) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of non-option equity instruments exercised by participants. + 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)(2) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + 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)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Definition Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + 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 (f)(2)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 Reference 2: 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.D.2) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 + Details
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