6. REGULATORY MATTERS

Regulatory Assets and Liabilities

Due to over or under recovery adjustments made in accordance with the FERC’s authoritative guidance and our cost-of-service recovery model, we recognize assets and liabilities for regulatory purposes. The assets and liabilities that we recognize for regulatory purposes are recorded on a net basis in “Other current assets” or “Accounts payable and other,” respectively, on our consolidated statements of financial position. These regulatory assets and liabilities are amortized on a straight-line basis over a one-year recovery period. Our over and under recovery revenue adjustments and net regulatory asset amortization for the years ended December 31, 2016, 2015, and 2014 are as follows:

	For the year ended December 31,
	2016		2015		2014
	(in millions)
Net regulatory asset balance at beginning of period	$	29.9	$	6.0	$	7.7
Current year under recovery adjustments		11.9		29.9		6.0
Amortization of prior year regulatory asset		(29.9)		(6.0)		(7.7)
Net regulatory asset balance at end of period	$	11.9	$	29.9	$	6.0

Other Contractual Obligations

Qualifying Volumes

We have certain contractual obligations with our customers in which a portion of the revenue earned on volumes above certain predetermined shipment levels, or qualifying volumes, are returned to the shippers through future rate adjustments. We record the liabilities associated with this contractual obligation in “Accounts payable and other,” on our consolidated statements of financial position. The amortization for this contractual obligation reflects the related transportation rate adjustment in the subsequent year. At December 31, 2016 and 2015, we had no qualifying volume liabilities related to the original Southern Access and Alberta Clipper agreements on our consolidated statements of financial position.

We amortize the liability on a straight line basis as an adjustment to revenue in the following year, reflecting the related rate adjustment. There was no amortization for qualifying volume liabilities for the years ended December 31, 2016 and 2015. For the year ended December 31, 2014, we amortized through revenue $6.1 million of qualifying volume liabilities on our consolidated statements of income with a corresponding amount reducing the contractual obligation on our consolidated statements of financial position.

Alberta Clipper Pipeline Property Taxes

A portion of the rates we charge our customers includes an estimate for annual property taxes. If the estimated property tax we collect from our customers is higher or lower than the actual property tax imposed, we are contractually obligated to refund to our customers or entitled to collect from our customers 50% of the property tax over or under recovery, respectively. At December 31, 2016 and 2015, we had $0.1 and $0.8 million, respectively, in property tax under recovery assets related to our Alberta Clipper Pipeline on our consolidated statements of financial position.

During 2015 and 2014, we incurred liabilities for contractual obligations with our customers on the Alberta Clipper Pipeline related to property taxes. As a result, in 2015 and 2014, we recorded a liability for the contractual amounts due back to our shippers with the corresponding amount as a reduction to revenue. We amortized the liability on a straight line basis as an adjustment to revenue in the following year. For the year ended December 31, 2016, we amortized through revenue $0.8 million of property tax under recovery assets, on our consolidated statements of income with a corresponding amount reducing the contractual obligation on our consolidated statements of financial position. For the years ended 2015 and 2014, we amortized through revenue $5.9 million and $6.9 million of property tax over recovery liabilities, respectively, on our consolidated statements of income with a corresponding amount reducing the contractual obligation on our consolidated statements of financial position.

Allowance for Equity Used During Construction

We are permitted to capitalize and recover costs for rate-making purposes that include allowance for equity used during construction, or AEDC. In connection with construction of the Eastern Access Projects, Line 3 Replacement and Mainline Expansion projects, we recorded $45.5 million, $70.3 million, and $57.2 million of “Allowance for equity used during construction” on our consolidated statements of income at December 31, 2016, 2015 and 2014, respectively, with corresponding amounts to “Property, plant and equipment, net” on our consolidated statements of financial position for the respective periods.