Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

Components of Accrued Revenue

The following table shows the components of Accrued Revenue as of December 31, 2017 and 2016.

Accrued Revenue (millions)	December 31,
	2017		2016
Regulatory Assets—Current	$	39.5	$	37.9
Unbilled Revenues		13.8		11.6
Total Accrued Revenue	$	53.3	$	49.5

Components of Exchange Gas Receivable

The following table shows the components of Exchange Gas Receivable as of December 31, 2017 and 2016.

Exchange Gas Receivable (millions)	December 31,
	2017		2016
Northern Utilities	$	5.4	$	7.8
Fitchburg		0.4		0.5
Total Exchange Gas Receivable	$	5.8	$	8.3

Components of Gas Inventory

The following table shows the components of Gas Inventory as of December 31, 2017 and 2016.

Gas Inventory (millions)	December 31,
	2017		2016
Natural Gas	$	0.4	$	0.3
Propane		0.1		0.2
Liquefied Natural Gas & Other		0.1		0.1
Total Gas Inventory	$	0.6	$	0.6

Regulatory Assets

Regulatory Assets consist of the following (millions)	December 31,
	2017		2016
Retirement Benefits	$	84.5	$	75.9
Energy Supply & Other Rate Adjustment Mechanisms		36.0		32.7
Deferred Storm Charges		7.2		9.6
Environmental		9.5		10.8
Income Taxes		6.5		7.3
Other		5.4		5.7
Total Regulatory Assets	$	149.1	$	142.0
Less: Current Portion of Regulatory Assets(1)		39.5		37.9
Regulatory Assets—noncurrent	$	109.6	$	104.1

⁽¹⁾  Reflects amounts included in Accrued Revenue on the Company’s Consolidated Balance Sheets and in the Accrued Revenue table shown above.

Regulatory Liabilities

Regulatory Liabilities consist of the following (millions)	December 31,
	2017		2016
Rate Adjustment Mechanisms	$	6.9	$	6.2
Gas Pipeline Refund (Note 8)		2.3		6.8
Income Taxes (Note 9)		48.9		—
Total Regulatory Liabilities		58.1		13.0
Less: Current Portion of Regulatory Liabilities		9.2		10.4
Regulatory Liabilities—noncurrent	$	48.9	$	2.6

Fair Value Amount of Derivative Assets Liabilities Offset in Regulatory Liabilities Assets

Fair Value Amount of Derivative Assets / Liabilities (millions) Offset in Regulatory Liabilities / Assets, as of:

		Fair Value
Description	Balance Sheet Location	December 31, 2017		December 31, 2016
Derivative Assets
Natural Gas Futures / Options Contracts	Prepayments and Other	$	—	$	0.1
Natural Gas Futures / Options Contracts	Other Noncurrent Assets		—		0.3
Total Derivative Assets		$	—	$	0.4
Derivative Liabilities
Natural Gas Futures / Options Contracts	Other Current Liabilities	$	—	$	—
Natural Gas Futures / Options Contracts	Other Noncurrent Liabilities		—		—
Total Derivative Liabilities		$	—	$	—

Regulatory Assets Liabilities and Reclassification from Regulatory Assets Liabilities into Purchased Gas

	Twelve Months Ended December 31,
	2017		2016
Amount of Loss / (Gain) Recognized in Regulatory Assets (Liabilities) for Derivatives:
Natural Gas Futures / Options Contracts	$	0.4	$	(0.1	)
Amount of Loss / (Gain) Reclassified into the Consolidated Statements of Earnings(1):
Cost of Gas Sales	$	—	$	0.3

⁽¹⁾  These amounts are offset in the Consolidated Statements of Earnings with Accrued Revenue and therefore there is no effect on earnings.

Fair Value of Marketable Securities

Changes in the fair value of these investments are recorded in Other Expense, net.

Fair Value of Marketable Securities (millions)	December 31,
	2017		2016
Equity Funds	$	2.1	$	1.1
Fixed Income Funds		1.5		0.8
Total Marketable Securities	$	3.6	$	1.9

Components of Energy Supply Obligations

The following discussion and table summarize the nature and amounts of the items recorded as Energy Supply Obligations (current portion) and Other Noncurrent Liabilities (noncurrent portion) on the Company’s Consolidated Balance Sheets.

	December 31,
Energy Supply Obligations consist of the following: (millions)	2017		2016
Current:
Exchange Gas Obligation	$	5.4	$	7.8
Renewable Energy Portfolio Standards		4.0		3.9
Power Supply Contract Divestitures		0.3		0.3
Total Energy Supply Obligations—Current	$	9.7	$	12.0
Noncurrent:
Power Supply Contract Divestitures	$	0.9	$	1.3
Total Energy Supply Obligations	$	10.6	$	13.3