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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 | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | Oct. 26, 2016
Class of Stock [Line Items] |  |  |  |  |
Aggregate purchase price |  |  | $ 472.5 |  |
Stock Repurchase Program Board Authorized Repurchases [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Shares repurchased (in shares) | 1.0 | 2.5 | 9.9 | 3.5 |
Aggregate purchase price | $ 50.0 | $ 150.0 | $ 470.6 | $ 209.1 |
Average purchase price per share (in dollars per share) | $ 48.62 | $ 59.83 | $ 47.48 | $ 60.54 |
Subsequent Event [Member] | Stock Repurchase Program Board Authorized Repurchases [Member] |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Remaining amount available for share repurchase |  |  |  |  | $ 315.9
Stock Repurchase Program, Authorized Amount |  |  |  |  | $ 250.0

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- Definition Total cost of shares repurchased divided by the total number of shares repurchased. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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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