FAIR VALUE MEASUREMENTS (Details) (USD $) In Thousands	9 Months Ended
Sep. 30, 2011	Dec. 31, 2010
Assets:
Derivative assets	$ 84,734	$ 34,188
Noncurrent investments available for sale	9,165	9,774
Deferred Compensation Plan	3,553	3,725
Supplemental retirement benefit trust life insurance policies (Note G)	5,153	5,665
Total financial assets, fair value	102,605	53,352
Liabilities:
Derivative liabilities	287,724	142,806
Net fair value assets/(liabilities)	(185,119)	(89,454)
Changes in fair value of assets and liabilities classified as level 3 [Roll Forward]
Net derivative assets/(liabilities)	(108,618)
Unrealized gains and (losses), net [Abstract]
Included in earnings	(422)
Included in other comprehensive income	64
Included in regulatory assets/(liabilities)	(94,014)
Net derivative assets/(liabilities)	(202,990)
Change in unrealized gains (losses), net relating to net derivative assets/(liabilities), still held as of September 30, 2011	(94,372)
Change in regulatory asset/liability balances [Roll Forward]
Net regulatory assets/(liabilities)	108,976
Unrealized (gains) and losses, net	94,014
Net regulatory assets/(liabilities)	202,990
Fair Value, Measurements, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets:
Derivative assets	0	0
Noncurrent investments available for sale	9,165	9,774
Deferred Compensation Plan	3,553	3,725
Supplemental retirement benefit trust life insurance policies (Note G)	5,153	5,665
Total financial assets, fair value	17,871	19,164
Liabilities:
Derivative liabilities	0	0
Net fair value assets/(liabilities)	17,871	19,164
Fair Value, Measurements, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Assets:
Derivative assets	0	0
Noncurrent investments available for sale	0	0
Deferred Compensation Plan	0	0
Supplemental retirement benefit trust life insurance policies (Note G)	0	0
Total financial assets, fair value	0	0
Liabilities:
Derivative liabilities	0	0
Net fair value assets/(liabilities)	0	0
Fair Value, Measurements, Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Assets:
Derivative assets	84,734	34,188
Noncurrent investments available for sale	0	0
Deferred Compensation Plan	0	0
Supplemental retirement benefit trust life insurance policies (Note G)	0	0
Total financial assets, fair value	84,734	34,188
Liabilities:
Derivative liabilities	287,724	142,806
Net fair value assets/(liabilities)	$ (202,990)	$ (108,618)

The increase (decrease) during the reporting period in the value of assets that are created when regulatory agencies permits public utilities to defer costs (revenues) to the balance sheet. This element is a the increase (decrease) of regulatory assets and liabilities combined.

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This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

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Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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The net amount of all regulatory assets less all regulatory liabilities as of the end of the period.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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