INVESTMENT IN ATC ROLL FORWARD (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Changes in equity method investments
Equity method investments balance at beginning of period			$ 512.2
Add: Earnings from equity method investment	23.1	22.2	68.2	65.5
Add: Capital contributions			10.2	24.0
Equity method investments balance at end of period	534.5		534.5
ATC
Investments in affiliates, at equity method
Equity method investment, ownership interest (as a percent)	34.00%		34.00%
Changes in equity method investments
Equity method investments balance at beginning of period	492.2	456.4	476.6	439.4
Add: Capital contributions	3.4	8.5	10.2	17.0
Less: Dividends received	17.8	17.3	52.7	50.9
Equity method investments balance at end of period	500.1	469.3	500.1	469.3
Regulated Operations
Changes in equity method investments
Add: Earnings from equity method investment	22.3	21.7	66.0	63.8
Regulated Operations \| Electric Transmission Investment
Changes in equity method investments
Add: Earnings from equity method investment	$ 22.3	$ 21.7	$ 66.0	$ 63.8

This item represents disclosure of the amount of dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporation; these investments are accounted for under the equity method of accounting. This element excludes distributions that constitute a return of investment, which are classified as investing activities.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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- Definition

This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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

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

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

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 18

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 11

-Article 7

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