Common Shareholders' Equity, Equity Rollforward (Details)	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common shareholders' equity, share rollforward
Common stock, shares issued ending balance	132,749,000us-gaap_CommonStockSharesIssued	132,711,000us-gaap_CommonStockSharesIssued
Treasury Common Shares
Common shareholders' equity, share rollforward
Treasury shares, ending balance	24,850,000	23,954,000
Common Shares
Common shareholders' equity, share rollforward
Common stock, shares issued beginning balance	125,545,000	125,512,000	125,502,000
Conversion of Series A Common Shares	25,000	33,000	10,000
Common stock, shares issued ending balance	125,570,000	125,545,000	125,512,000
Common Shares \| Treasury Common Shares
Common shareholders' equity, share rollforward
Treasury shares, beginning balance	23,954,000	24,641,000	24,165,000
Repurchase of shares	1,542,000	339,000	868,000
Dividend reinvestment, incentive and compensation plans - Treasury shares	(646,000)	(1,026,000)	(392,000)
Treasury shares, ending balance	24,850,000	23,954,000	24,641,000
Common Shares \| Series A Share Conversion
Common shareholders' equity, other disclosures
Shares reserved	7,178,943
Common Shares \| Tax-Deferred Savings Plan
Common shareholders' equity, other disclosures
Shares reserved	90,341
Series A Common Shares
Common shareholders' equity, share rollforward
Common stock, shares issued beginning balance	7,166,000	7,160,000	7,119,000
Conversion of Series A Common Shares	(25,000)	(33,000)	(10,000)
Dividend reinvestment, incentive and compensation plans	38,000	39,000	51,000
Common stock, shares issued ending balance	7,179,000	7,166,000	7,160,000

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Aggregate number of common shares reserved for future issuance.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

Reference 1: 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)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 30

-Article 5

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The number of new shares issued in the conversion of stock in a noncash (or part noncash) transaction. Noncash is defined as transactions during a period that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

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Number of shares issued during the period from a dividend reinvestment plan (DRIP). A dividend reinvestment plan allows the shareholders to reinvest dividends paid to them by the entity on new issues of stock by the entity.

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Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding.

+ 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

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28,29)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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-Number 210

-Section 02

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Number of shares that have been repurchased during the period and are being held in treasury.

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