Share-Based Compensation Plans (Narrative) (Details) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($) plans $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of share-based compensation plans \| plans	1
Number of options granted in period \| shares	488	0
Weighted average grant date fair value of options granted \| $ / shares	$ 14.42		$ 19.52
Total cash received from options exercised	$ 4.6	$ 10.0	$ 4.5
Total intrinsic value of options exercised	8.2	$ 10.7	$ 4.2
Total unrecognized compensation cost related to unvested share-based compensation arrangements	$ 14.2
Period for recognition (in years)	5 years 5 months
Weighted-average period for recognition	1 year 11 months
Performance Incentive Plan 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized \| shares	2,450,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average grant-date fair value of stock awarded \| $ / shares	$ 112.88	$ 139.31	$ 152.70
Total vesting-date fair value of shares vested during the year	$ 9.7	$ 12.5	$ 13.8
Grants of common shares and options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Term	3 years
Grants of common shares and options \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Term	7 years
Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (in years)	10 years

Number Of Share Based Compensation Plans with outstanding grants

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Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Years

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Unrecognized cost of unvested share-based compensation awards.

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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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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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).

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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.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Net number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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