Borrowings and Other Financing Instruments, Issuances of Common Stock (Details) (At-the-Market Program, USD $) Share data in Millions, unless otherwise specified	1 Months Ended
Mar. 31, 2013	Jun. 30, 2013
At-the-Market Program
Issuances of Common Stock [Abstract]
Maximum aggregate gross sales price of common stock that can be offered and sold	$ 400,000,000
Shares of common stock issued (in shares)		7.7
Net cash proceeds from issuance of common stock		223,100,000
Fees and commissions		$ 2,300,000

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.

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)

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

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 30

-Article 5

+ Details

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- Definition

The cumulative fees and commissions paid to issue additional shares of common stock under an at-the-market offering program.

+ References

No definition available.

+ Details

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- Definition

The cumulative net cash proceeds from the additional capital contribution to the entity under an at-the-market offering program.

+ References

No definition available.

+ Details

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- Details

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- Definition

The maximum aggregate gross sales price of shares of common stock that can be offered and sold from time to time through an at-the-market offering program.

+ References

No definition available.

+ Details

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