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Company's Liability for Environmental Obligations (Detail) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Dec. 31, 2019
Environmental Exit Cost [Line Items] |  |  |
Total Balance at Beginning of Period | $ 2.7 | $ 2.0 |
Additions | 0.0 | 0.1 |
Less: Payments / Reductions | 0.5 | 0.1 |
Total Balance at End of Period | 2.2 | 2.0 |
Less: Current Portion | 0.3 | 0.6 | $ 0.6
Noncurrent Balance at End of Period | 1.9 | 1.4 | $ 2.1
Fitchburg Gas and Electric Light Company |  |  |
Environmental Exit Cost [Line Items] |  |  |
Total Balance at Beginning of Period |  |  |
Additions |  |  |
Less: Payments / Reductions |  |  |
Total Balance at End of Period |  |  |
Less: Current Portion |  |  |
Noncurrent Balance at End of Period |  |  |
Northern Utilities Inc |  |  |
Environmental Exit Cost [Line Items] |  |  |
Total Balance at Beginning of Period | 2.7 | 2.0 |
Additions | 0.0 | 0.1 |
Less: Payments / Reductions | 0.5 | 0.1 |
Total Balance at End of Period | 2.2 | 2.0 |
Less: Current Portion | 0.3 | 0.6 |
Noncurrent Balance at End of Period | $ 1.9 | $ 1.4 |

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