DPU Safety And Reliability Programs (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Notes To Consolidated Financial Statements [Abstract]
Cumulative Costs Associated With Cpsl Program At Nstar Electric	$ 90.0
Cpsl Annual Revenue Per Annum From Comprehensive Settlement Agreement	$ 15.0

The comprehensive settlement agreement with the Massachusetts AG stipulates a revenue stream of up to $15 million per annum for 2012 to 2015 in order to continue the program.

No definition available.

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