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Company's Liability for Environmental Obligations (Detail) - USD ($) $ in Millions | 12 Months Ended |  |
--- | --- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017
Environmental Exit Cost [Line Items] |  |  |  |
Total Balance at Beginning of Period | $ 2.1 | $ 1.9 |  |
Additions | 0.3 | 0.4 |  |
Less: Payments / Reductions | 0.4 | 0.2 |  |
Total Balance at End of Period | 2.0 | 2.1 |  |
Less: Current Portion |  |  | $ 0.6 | $ 0.5
Noncurrent Balance |  |  | 1.4 | 1.6
Total Balance at End of Period | 2.1 | 1.9 | 2.0 | 2.1
Fitchburg Gas and Electric Light Company |  |  |  |
Environmental Exit Cost [Line Items] |  |  |  |
Total Balance at Beginning of Period | 0.1 | 0.1 |  |
Less: Payments / Reductions | 0.1 |  |  |
Total Balance at End of Period |  | 0.1 |  |
Noncurrent Balance |  |  |  | 0.1
Total Balance at End of Period | 0.1 | 0.1 |  | 0.1
Northern Utilities Inc |  |  |  |
Environmental Exit Cost [Line Items] |  |  |  |
Total Balance at Beginning of Period | 2.0 | 1.8 |  |
Additions | 0.3 | 0.4 |  |
Less: Payments / Reductions | 0.3 | 0.2 |  |
Total Balance at End of Period | 2.0 | 2.0 |  |
Less: Current Portion |  |  | 0.6 | 0.5
Noncurrent Balance |  |  | 1.4 | 1.5
Total Balance at End of Period | $ 2.0 | $ 1.8 | $ 2.0 | $ 2.0

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