INVESTMENT IN ATC - ROLL FORWARD (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Changes in equity method investments
Equity method investments balance at beginning of period	$ 540.9
Add: Earnings from equity method investment	22.9	22.3
Add: Capital contributions	5.1	1.7
Equity method investments balance at end of period	548.1
ATC
Investments in affiliates, at equity method
Equity method investment, ownership interest (as a percent)	34.00%
Changes in equity method investments
Equity method investments balance at beginning of period	508.4	476.6
Add: Earnings from equity method investment	22.5	21.7
Add: Capital contributions	5.1	1.7
Less: Dividends received	18.4	17.3
Equity method investments balance at end of period	$ 517.6	$ 482.7

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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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This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized.

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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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The cash outflow associated with the acquisition of or advances to an entity that is related to it but not strictly controlled (for example, an unconsolidated subsidiary, affiliate, and joint venture or equity method investment) or the acquisition of an additional interest in a subsidiary (controlled entity).

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