Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2016

Components of Accrued Revenue

The following table shows the components of Accrued Revenue as of December 31, 2016 and 2015.

Accrued Revenue (millions)	December 31,
	2016		2015
Regulatory Assets—Current	$	37.9	$	26.8
Unbilled Revenues		11.6		11.6
Total Accrued Revenue	$	49.5	$	38.4

Components of Exchange Gas Receivable

The following table shows the components of Exchange Gas Receivable as of December 31, 2016 and 2015.

Exchange Gas Receivable (millions)	December 31,
	2016		2015
Northern Utilities	$	7.8	$	10.3
Fitchburg		0.5		0.8
Total Exchange Gas Receivable	$	8.3	$	11.1

Components of Gas Inventory

The following table shows the components of Gas Inventory as of December 31, 2016 and 2015.

Gas Inventory (millions)	December 31,
	2016		2015
Natural Gas	$	0.3	$	0.3
Propane		0.2		0.3
Liquefied Natural Gas & Other		0.1		0.2
Total Gas Inventory	$	0.6	$	0.8

Regulatory Assets

Regulatory Assets consist of the following (millions)	December 31,
	2016		2015
Retirement Benefits	$	75.9	$	64.7
Energy Supply & Other Regulatory Tracker Mechanisms		32.7		21.3
Deferred Storm Charges		9.6		15.4
Environmental		10.8		11.2
Income Taxes		7.3		8.5
Other		5.7		5.3
Total Regulatory Assets	$	142.0	$	126.4
Less: Current Portion of Regulatory Assets(1)		37.9		26.8
Regulatory Assets—noncurrent	$	104.1	$	99.6

⁽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,
	2016		2015
Regulatory Tracker Mechanisms	$	6.2	$	8.0
Gas Pipeline Refund (Note 8)		6.8		15.7
Total Regulatory Liabilities		13.0		23.7
Less: Current Portion of Regulatory Liabilities		10.4		15.6
Regulatory Liabilities—noncurrent	$	2.6	$	8.1

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, 2016		December 31, 2015
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,
	2016			2015
Amount of Loss / (Gain) Recognized in Regulatory Assets (Liabilities) for Derivatives:
Natural Gas Futures / Options Contracts	$	(0.1	)	$	0.3
Amount of Loss / (Gain) Reclassified into the Consolidated Statements of Earnings(1):
Cost of Gas Sales	$	0.3		$	0.2

⁽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

These investments are valued based on quoted prices from active markets and are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied. Changes in the fair value of these investments are recorded in Other Expense, net.

Fair Value of Marketable Securities (millions)	December 31,
	2016		2015
Equity Funds	$	1.1	$	0.4
Fixed Income Funds		0.8		0.3
Total Marketable Securities	$	1.9	$	0.7

Components of Energy Supply Obligations

	December 31,
Energy Supply Obligations consist of the following: (millions)	2016		2015
Current:
Exchange Gas Obligation	$	7.8	$	10.3
Renewable Energy Portfolio Standards		3.9		4.0
Power Supply Contract Divestitures		0.3		0.3
Total Energy Supply Obligations—Current	$	12.0	$	14.6
Noncurrent:
Power Supply Contract Divestitures	$	1.3	$	1.6
Total Energy Supply Obligations	$	13.3	$	16.2