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Shareholders' Equity (Share Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Nov. 30, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Class of Stock [Line Items] |  |  |  |
Aggregate purchase price |  | $ 44.7 | $ 100.0 | $ 434.9
Treasury Stock, Shares, Retired | 18.0 |  |  |
Stock Repurchase Program Board Authorized Repurchases [Member] |  |  |  |
Class of Stock [Line Items] |  |  |  |
Shares repurchased (in shares) |  | 1.3 | 2.1 | 10.1
Aggregate purchase price |  | $ 44.7 | $ 100.0 | $ 434.9
Average purchase price per share (in dollars per share) |  | $ 35.51 | $ 47.58 | $ 42.99
Remaining amount available for share repurchase |  | $ 219.0 |  |

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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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