Business and Basis of Presentation (Schedule of Prior Year Amounts Recast Affected by Cumulative Adjustment in Shareholders' Equity) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Retained earnings	$ 905.7	$ 859.9	$ 829.8	$ 727.6	$ 680.3	$ 598.2
Total Shareholders' Equity	$ 243.1	245.1	226.0	368.9	368.6	384.1
As Reported [Member]
Error Corrections And Prior Period Adjustments Restatement [Line Items]
Retained earnings		895.1	865.0	762.8	715.5	633.4
Total Shareholders' Equity		$ 280.3	$ 261.2	$ 404.1	$ 403.8	$ 419.3

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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