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Stockholders' Equity and Earnings Per Common Share Treasury Stock Transactions (Details) - USD ($) shares in Millions, $ in Millions | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Equity, Class of Treasury Stock |  |
Number of Treasury Shares Repurchased | 1.9 | 2.1
Cost of Shares Repurchased | $ 100.2 | $ 100.0
Commission Paid on Common Stock Repurchased | 0.2 | $ 0.0
Repurchase Program Authorized in May 2017 |  |
Equity, Class of Treasury Stock |  |
Authorized Stock Repurchases | 750.0 |
Remaining Authorized Share Repurchases | 412.8 |
Repurchase Program Authorized in May 2016 |  |
Equity, Class of Treasury Stock |  |
Authorized Stock Repurchases | $ 750.0 |

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- Definition Number of shares that have been repurchased during the period and are being held in treasury. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644 + Details
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