REGULATORY ASSETS AND LIABILITIES

We recorded a $2,450 million change in our deferred taxes for our regulated utilities due to the enactment of the Tax Legislation, which resulted in both an increase to income tax related regulatory liabilities as well as a decrease to certain existing income tax related regulatory assets represented in Income tax related items in the table below. The $2,450 million change in our deferred taxes represents our estimate of the tax benefit that will be returned to ratepayers through future refunds, bill credits, riders, or reductions in other regulatory assets. See Note 13, Income Taxes, for more information on the Tax Legislation.

The following regulatory assets were reflected on our balance sheets as of December 31:



(in millions)	2017		2016		See Note
Regulatory assets ^{(1) (2)}
Unrecognized pension and OPEB costs ⁽³⁾	$	1,142.0	$	1,252.1	17
Environmental remediation costs ⁽⁴⁾	676.6		702.7		21
SSR	298.9		188.1		23
Electric transmission costs	221.0		234.1		23
AROs	192.2		179.2		7
We Power generation ⁽⁵⁾	71.3		54.1
Uncollectible expense ⁽⁶⁾	35.1		25.6		1(d)
Energy efficiency programs ⁽⁷⁾	24.6		36.7
Income tax related items	15.7		285.1		13
Other, net	163.0		180.6
Total regulatory assets	$	2,840.4	$	3,138.3

Balance Sheet Presentation
Current assets ⁽⁸⁾	$	37.2	$	50.4
Regulatory assets	2,803.2		3,087.9
Total regulatory assets	$	2,840.4	$	3,138.3


⁽¹⁾	Based on prior and current rate treatment, we believe it is probable that our utilities will continue to recover from customers the regulatory assets in the table.

⁽²⁾

As of December 31, 2017, we had $116.9 million of regulatory assets not earning a return and $261.1 million of regulatory assets earning a return based on short-term interest rates. The regulatory assets not earning a return primarily relate to certain environmental remediation costs, the recovery of which depends on the timing of the actual expenditures, as well as certain unrecognized pension and OPEB costs, unamortized loss on reacquired debt, and plant-related costs. The other regulatory assets in the table either earn a return or the cash has not yet been expended, in which case the regulatory assets are offset by liabilities.


⁽³⁾	Represents the unrecognized future pension and OPEB costs resulting from actuarial gains and losses on defined benefit and OPEB plans. We are authorized recovery of this regulatory asset over the average remaining service life of each plan.


⁽⁴⁾	As of December 31, 2017, we had not yet made cash expenditures for $617.4 million of these environmental remediation costs.


⁽⁵⁾	Represents amounts recoverable from customers related to WE's costs of the generating units leased from We Power, including subsequent capital additions.


⁽⁶⁾	Represents amounts recoverable from customers related to our uncollectible expense tracking mechanisms and riders. These mechanisms allow us to recover or refund the difference between actual uncollectible write-offs and the amounts recovered in rates.


⁽⁷⁾	Represents amounts recoverable from customers related to programs at the utilities designed to meet energy efficiency standards.


⁽⁸⁾	Short-term regulatory assets are recorded in accounts receivable and unbilled revenues on our balance sheets.

The following regulatory liabilities were reflected on our balance sheets as of December 31:



(in millions)	2017		2016		See Note
Regulatory liabilities
2017 Tax Legislation impact and income tax related	$	2,134.1	$	—	13
Removal costs ⁽¹⁾	1,294.9		1,262.7
Unrecognized pension and OPEB costs ⁽²⁾	114.2		63.0		17
Mines deferral ⁽³⁾	95.1		70.2
Energy costs refundable through rate adjustments ⁽⁴⁾	42.0		88.7
Uncollectible expense ⁽⁵⁾	24.7		36.1		1(d)
Derivatives	11.0		41.1		1(q)
Other, net	44.4		35.4
Total regulatory liabilities	$	3,760.4	$	1,597.2

Balance Sheet Presentation
Current liabilities	$	41.8	$	33.4
Regulatory liabilities	3,718.6		1,563.8
Total regulatory liabilities	$	3,760.4	$	1,597.2


⁽¹⁾	Represents amounts collected from customers to cover the cost of future removal of property, plant, and equipment.


⁽²⁾	Represents the unrecognized future pension and OPEB costs resulting from actuarial gains and losses on defined benefit and OPEB plans. We will amortize this regulatory liability into net periodic benefit cost over the average remaining service life of each plan.


⁽³⁾	Represents the deferral of revenues less the associated cost of sales related to sales to the mines, which were not included in the 2015 rate order. We intend to request that this deferral be applied for the benefit of Wisconsin retail electric customers in a future rate proceeding.


⁽⁴⁾	Represents energy costs that will be refunded to customers in the future.


⁽⁵⁾	Represents amounts refundable to customers related to our uncollectible expense tracking mechanisms and riders. These mechanisms allow us to recover or refund the difference between actual uncollectible write-offs and the amounts recovered in rates.