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Shareholders' Equity (Shares Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 | Mar. 31, 2018
Class of Stock [Line Items] |  |
Aggregate purchase price | $ 33.5 | $ 26.6
Stock Repurchase Program Board Authorized Repurchases [Member] |  |
Class of Stock [Line Items] |  |
Shares repurchased (in shares) | 1.0 | 0.5
Aggregate purchase price | $ 33.5 | $ 26.6
Average purchase price per share (in dollars per share) | $ 34.34 | $ 48.38
Remaining amount available for share repurchase | $ 230.2 |

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- Definition Amount remaining of a stock repurchase plan authorized. + References No definition available. + Details
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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655 + Details
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