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Common Shareholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended |  | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011 | Nov. 17, 2006 | Dec. 31, 2013 Common Stock | Dec. 31, 2012 Common Stock | Dec. 31, 2011 Common Stock | Dec. 31, 2013 Restricted Stock | Dec. 31, 2012 Restricted Stock | Dec. 31, 2011 Restricted Stock | Dec. 31, 2012 Performance Shares [Member] | Dec. 31, 2013 Common Stock | Dec. 31, 2012 Common Stock | Dec. 31, 2011 Common Stock | Dec. 31, 2011 Combination Two [Member] STO | Dec. 31, 2011 Combination Two [Member] Common Stock | Dec. 31, 2013 General Board Authorization [Member] | Dec. 31, 2012 General Board Authorization [Member] | Dec. 31, 2011 General Board Authorization [Member] | Dec. 31, 2010 General Board Authorization [Member] | Dec. 31, 2013 Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member] Combination Three [Member] | Dec. 31, 2012 Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member] Combination Three [Member] | Dec. 31, 2011 Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member] Combination Three [Member] | Dec. 31, 2012 Tender Offer [Member] Combination Two [Member] | Dec. 31, 2012 Tender Offer [Member] Combination Two [Member] Common Stock
Common Shares Repurchased and Retired [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Authorized repurchase of common shares |  | 2,600,000 |  | 1,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Additional authorized repurchase of common shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 545,496 | 1,000,000 |  | 600,000 |  |  |  |  |
Common shares repurchased and retired during the period |  | 1,329,640 |  |  |  |  |  |  |  |  |  | 141,535 | 1,329,640 | 646,502 |  | 332,346 | 140,000 | 502,801 | 313,967 |  |  |  |  |  | 816,829
Number of Modified Dutch Auction |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |
Value of common shares repurchased and retired during the period | $ 79.8 | $ 669.1 | $ 253.0 |  | $ 79.8 | $ 669.1 | $ 253.0 |  |  |  |  |  |  |  | $ 138.8 |  | $ 78.9 | $ 256.0 | $ 114.0 |  |  |  |  | $ 408.6 |
Value of each common share repurchased and retired during the period (in dollars per share) | $ 564.00 | $ 503.00 | $ 390.00 |  |  |  |  |  |  |  |  |  |  |  | $ 417.55 |  | $ 564.00 | $ 508.00 | $ 364.00 |  | $ 1,535.00 | $ 10,010.00 | $ 189.00 | $ 500.00 |
Stock Issued During Period, Shares, New Issues | 27,310 | 44,054 | 29,432 |  |  |  |  | 25,720 | 700 |  | 9,577 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common shares, issued shares | 6,176,739 | 6,290,964 |  |  |  |  |  |  | 32,160 | 27,250 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Common Shares Issued [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Shares issued to directors (in shares) | 1,590 | 1,617 | 2,182 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends, Common Stock [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash dividends declared and paid | $ 6.2 | $ 6.6 | $ 8.0 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Dividends delared and paid (in dollars per share) | $ 1.00 | $ 1.00 | $ 1.00 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Number of shares that have been repurchased and retired during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: 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=6928386&loc=d3e21463-112644 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29, 30 -Article 5 + Details
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