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Risk Management Activities (Narrative) (Details) (USD $)
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6 Months Ended | 9 Months Ended | 6 Months Ended | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Jun. 30, 2011
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Sep. 30, 2005
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Sep. 30, 2003
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Dec. 31, 2010
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Dec. 31, 2008
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Sep. 16, 2005
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Jul. 22, 2003
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Sep. 16, 2005
5.25% - Due September 15, 2017 [Member]
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Sep. 16, 2005
5.45% - Due September 15, 2020 [Member]
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Jun. 30, 2011
5.33% - Due June 30, 2027 [Member]
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Jun. 30, 2011
6.00% - Due June 30, 2032 [Member]
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Jun. 30, 2011
Physical Sales Contracts Marked to Market [Member]
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Dec. 31, 2010
Physical Sales Contracts Marked to Market [Member]
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Jun. 30, 2011
Financial Derivative Contracts Marked to Market [Member]
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Jan. 31, 2011
Financial Derivative Contracts Marked to Market [Member]
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Dec. 31, 2010
Financial Derivative Contracts Marked to Market [Member]
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| Reserves against physical sale contract derivatives | $ 3,800,000 | $ 6,400,000 | ||||||||||||||
| Fair value of physical sales contracts and derivative contracts | 118,100,000 | 154,400,000 | (114,900,000) | 10,300,000 | (137,500,000) | |||||||||||
| Outstanding debt | 7,200,000,000 | |||||||||||||||
| Outstanding debt subject to interest rate fluctuations | 500,000,000 | |||||||||||||||
| Notional amount of interest rate swap agreements | 420,000,000 | 900,000,000 | 500,000,000 | |||||||||||||
| Number of counterparties in swap agreement | 4 | |||||||||||||||
| Period of swap agreement | 11 Years | |||||||||||||||
| Fixed interest rate under swap agreement | 5.40% | |||||||||||||||
| Floating interest amount, average interest addition | 0.78% | |||||||||||||||
| Face amount of notes | 725,000,000 | 1,000,000,000 | 375,000,000 | 350,000,000 | ||||||||||||
| Debt instrument interest rate stated percentage | 5.25% | 5.45% | 5.33% | 6.00% | ||||||||||||
| Debt instrument maturity date | Jun. 30, 2027 | Jun. 30, 2032 | ||||||||||||||
| Effective interest rate of debt instrument | 5.67% | 5.88% | ||||||||||||||
| Number of counterparties in swap agreement settled | 6 | |||||||||||||||
| Payment for settlement of interest rate swap | 35,500,000 | |||||||||||||||
| Forward starting interest rate swap settlement amount | 12,100,000 | |||||||||||||||
| Percentage of interest in Millennium | 47.50% | |||||||||||||||
| Unrealized loss on terminated interest rate swaps | 20,600,000 | |||||||||||||||
| Loss recognized in income statement classified in accumulated other comprehensive income(loss) | 400,000 | |||||||||||||||
| Contingent collateral requirement | 2,000,000 | |||||||||||||||
| Cash on deposit with brokers for margin requirements | $ 154,400,000 | $ 198,300,000 | ||||||||||||||