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Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Loss Contingencies [Line Items]
Component of estimated minimum liability for remediation of manufactured gas plant site	$ 16.0
Component of estimated maximum liability for remediation of manufactured gas plant site	20.2
Former Manufactured Gas Plant Site [Member]
Loss Contingencies [Line Items]
Component of estimated minimum liability for remediation of manufactured gas plant site	$ 14.3

The estimated maximum amount of possible loss from the contingency.

The estimated minimum amount of possible loss from the contingency.