Common Equity - Share Repurchase Program (Details) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2015	Sep. 30, 2014
Class of Stock [Line Items]
Stock Repurchased During Period, Shares	1.3	1.9
Stock Repurchased During Period, Value	$ 66.1	$ 84.2
Share Repurchase Plan, 2013 [Member]
Class of Stock [Line Items]
Stock Repurchase Program, Authorized Amount	$ 300.0
Stock Repurchased During Period, Shares	0.0	0.4
Stock Repurchased During Period, Value	$ 0.0	$ 18.6
Share Repurchases to Fulfill Exercised Stock Options and Restricted Stock Awards [Member]
Class of Stock [Line Items]
Stock Repurchased During Period, Shares	1.3	1.5
Stock Repurchased During Period, Value	$ 66.1	$ 65.6

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- Definition

Amount of stock repurchase plan authorized.

+ References

No definition available.

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- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

Reference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

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- Definition

Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ References

Reference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30, 31

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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