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Kingston Fossil Plant Ash Spill Kingston Fossil Plant Ash Spill (Details) Cubic_yards in Millions, $ in Millions	1 Months Ended	12 Months Ended	42 Months Ended
	Nov. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2008 Dredge_cells Cubic_yards
Kingston Fossil Plant Ash Spill
Number of dredge cells that failed | Dredge_cells				1
Cubic yards of water and coal fly ash that flowed out of the cell | Cubic_yards				5
Period collected in rates		15 years
Kingston cleanup amounts spent to date		$ 1,100	$ 1,100
Remaining estimated Kingston liability		6	6
Kingston insurance recoveries		$ 63	$ 336
Scenario, Forecast [Member]
Kingston Fossil Plant Ash Spill
Kingston insurance recoveries	$ 7

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The amount of cubic yards of water and coal fly ash that flowed out of the cell.

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Amounts spent since the event through a certain date for the Kingston Ash Spill cleanup effort.

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The number of dredge cells that failed.

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The time period that the expense is collected in rates.

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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The amount recovered from insurance. These recoveries reduce costs and losses that are reported as a separate line item under operating expenses.

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