Gallons of diesel fuel purchased annually.

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- Definition

Percentage Of Trading Portfolio Realized

+ Details

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- Definition

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12

+ Details

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- Definition

The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=6935481&loc=d3e41678-113959
-Subparagraph (b)

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- Definition

The percentage of expected requirements covered by the aggregate notional amount of derivative contracts expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract as a percentage of expected need.

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- Definition

The estimated net amount of unrealized gains or losses on price risk cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 45
-Subparagraph b(2)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6887037&loc=d3e80748-113994

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- Definition

The net gain (loss) on trading activities (including both derivative and nonderivative instruments) recognized in the statement of financial performance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4F
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5624186-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
-Subparagraph c
-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 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Paragraph 205H
-Number 133
-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.

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Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended														6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 One Year from Balance Sheet Date [Member] Coal [Member]	Jun. 30, 2011 One Year from Balance Sheet Date [Member] Coal [Member] Coal Purchases [Member]	Jun. 30, 2011 More than One and within Two Years from Balance Sheet Date [Member] Coal [Member]	Jun. 30, 2011 More than One and within Two Years from Balance Sheet Date [Member] Coal [Member] Coal Purchases [Member]	Jun. 30, 2011 More than Two and within Three Years from Balance Sheet Date [Member] Coal [Member]	Jun. 30, 2011 More than Three and within Four Years from Balance Sheet Date [Member] Coal [Member]	Jun. 30, 2011 More than Four and within Five Years from Balance Sheet Date [Member] Coal [Member]	Jun. 30, 2011 Heating Oil [Member]	Jun. 30, 2011 Current Assets [Member]	Dec. 31, 2010 Current Assets [Member]	Jun. 30, 2011 Year One [Member]	Jun. 30, 2011 Year Two [Member]	Jun. 30, 2011 Minimum Purchase [Member]	Jun. 30, 2011 Maximum Purchase [Member]
Gallons of diesel fuel purchased annually																	75,000,000	85,000,000
Percent of diesel purchases hedged															70.00%	41.00%
Quantities under derivative contracts					1,300,000	600,000	1,300,000	200,000	700,000	1,400,000	700,000	66,800,000
Percentage of trading portfolio realized															50.00%	50.00%
Current asset for the right to reclaim cash collateral													$ 9.2	$ 10.3
Net unrealized and realized gains (losses) related to trading portfolio	(2.3)	(1.1)	0.5	(2.1)
Gain on derivative contracts designated as hedge instruments in cash flow hedges to be reclassified from OCI into earnings during the next twelve months	$ 17.9		$ 17.9