The following table presents our regulatory assets and regulatory liabilities at December 31, 2018 and 2017:



	2018									2017
	Ameren Missouri			Ameren Illinois			Ameren				Ameren Missouri			Ameren Illinois			Ameren
Regulatory assets:
Under-recovered FAC^(a)	$	3		$	—		$	3			$	47		$	—		$	47
Under-recovered PGA^(b)	—			7			7				1			13			14
MTM derivative losses^(c)	19			197			216				12			217			229
IEIMA revenue requirement reconciliation adjustment^(d)(e)	—			70			70				—			78			78
FERC revenue requirement reconciliation adjustment^(f)	—			16			30				—			25			37
Under-recovered VBA rider^(g)	—			—			—				—			15			15
Pension and postretirement benefit costs^(h)	103			149			252				84			215			299
Income taxes⁽ⁱ⁾	119			68			185				139			56			197
Callaway costs^(e)(j)	22			—			22				25			—			25
Unamortized loss on reacquired debt^(k)	58			40			98				61			49			110
Environmental cost riders^(l)	—			148			148				—			173			173
Storm costs^(e)(m)	—			13			13				—			10			10
Demand-side costs before the MEEIA implementation^(e)(n)	5			—			5				11			—			11
Workers’ compensation claims^(o)	4			7			11				5			7			12
Construction accounting for pollution control equipment^(e)(p)	16			—			16				18			—			18
Solar rebate program^(e)(q)	14			—			14				31			—			31
FEJA energy-efficiency riders^(e)(r)	—			136			136				—			41			41
Other	17			18			35				17			10			27
Total regulatory assets	$	380		$	869		$	1,261			$	451		$	909		$	1,374
Less: current regulatory assets	(14		)	(110		)	(134		)		(56		)	(87		)	(144		)
Noncurrent regulatory assets	$	366		$	759		$	1,127			$	395		$	822		$	1,230
Regulatory liabilities:
Over-recovered FAC^(a)	$	34		$	—		$	34			$	4		$	—		$	4
Over-recovered Illinois electric power costs^(b)	—			12			12				—			16			16
Over-recovered PGA^(b)	7			3			10				—			1			1
Over-recovered VBA rider^(g)	—			8			8				—			—			—
MTM derivative gains^(c)	5			3			8				16			—			16
FERC revenue requirement reconciliation adjustment^(f)	—			17			19				—			—			—
Energy-efficiency riders^(s)	19			3			22				2			40			42
Estimated refund for FERC complaint case^(t)	—			26			44				—			25			42
Income taxes⁽ⁱ⁾	1,484			843			2,413				1,392			842			2,323
Asset removal costs^(u)	1,027			774			1,811				995			725			1,725
AROs^(v)	175			—			175				223			—			223
Pension and postretirement benefit costs tracker^(w)	43			—			43				35			—			35
Renewable energy credits and zero emission credits^(x)	—			102			102				—			58			58
Excess income taxes collected in 2018^(y)	60			—			60				—			—			—
Other	13			12			25				16			14			30
Total regulatory liabilities	$	2,867		$	1,803		$	4,786			$	2,683		$	1,721		$	4,515
Less: current regulatory liabilities	(68		)	(62		)	(149		)		(19		)	(92		)	$	(128	)
Noncurrent regulatory liabilities	$	2,799		$	1,741		$	4,637			$	2,664		$	1,629		$	4,387


(a)	Under-recovered or over-recovered fuel costs to be recovered or refunded through the FAC. Specific accumulation periods aggregate the under-recovered or over-recovered costs over four months, any related adjustments that occur over the following four months, and the recovery from, or refund to, customers that occurs over the next eight months.


(b)	Under-recovered or over-recovered costs from utility customers. Amounts will be recovered from, or refunded to, customers within one year of the deferral.


(c)	Deferral of commodity-related derivative MTM losses or gains. See Note 7 – Derivative Financial Instruments for additional information.


(d)	The difference between Ameren Illinois’ electric distribution service annual revenue requirement calculated under the performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. Any under-recovery or over-recovery will be recovered from, or refunded to, customers with interest within two years.


(e)	These assets earn a return.


(f)	Ameren Illinois’ and ATXI’s annual revenue requirement reconciliation calculated pursuant to the FERC’s electric transmission formula ratemaking framework. Any under-recovery or over-recovery will be recovered from, or refunded to, customers within two years.


(g)	Under-recovered or over-recovered natural gas revenue caused by sales volume deviations from weather normalized sales approved by the ICC in rate regulatory reviews. Each year’s amount will be recovered from, or refunded to, customers from April through December of the following year.


(h)	These costs are being amortized in proportion to the recognition of prior service costs (credits) and actuarial losses (gains) attributable to Ameren’s pension plan and postretirement benefit plans. See Note 10 – Retirement Benefits for additional information.

(i)

The regulatory assets represent deferred income taxes that will be recovered from customers related to the equity component of allowance for funds used during construction and the effects of tax rate changes from the TCJA and the increased income tax rate in Illinois. The regulatory liabilities represent deferred income taxes that will be refunded to customers related to depreciation differences, other tax liabilities, and the unamortized portion of investment tax credits recorded at rates in excess of current statutory rates. Amounts associated with the equity component of allowance for funds used during construction, and the unamortized portion of investment tax credits will be amortized over the expected life of the related assets. The amortization periods for depreciation differences are determined in rate orders by the applicable regulators and range from 7 to 60 years. See Note 12 – Income Taxes for amounts related to the revaluation of deferred income taxes under the TCJA.


(j)	Ameren Missouri’s Callaway energy center operations and maintenance expenses, property taxes, and carrying costs incurred between the plant in-service date and the date the plant was reflected in rates. These costs are being amortized over the original remaining life of the energy center.


(k)	Losses related to reacquired debt. These amounts are being amortized over the lives of the related new debt issuances or the original lives of the old debt issuances if no new debt was issued.


(l)	The recoverable portion of accrued environmental site liabilities that will be collected from electric and natural gas customers through ICC-approved cost recovery riders. The period of recovery will depend on the timing of remediation expenditures. See Note 14 – Commitments and Contingencies for additional information.


(m)	Storm costs from 2015, 2016, and 2018 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in the year the storm occurred.

(n)

Demand-side costs incurred prior to implementation of the MEEIA in 2013, including the costs of developing, implementing, and evaluating customer energy-efficiency and demand response programs. The MoPSC’s March 2017 electric rate order modified certain amortization periods for these costs. Costs incurred from May 2008 through September 2008, and from January 2010 through July 2012, are being amortized over a two-year period that began in April 2017. Costs incurred from October 2008 through December 2009 are no longer being amortized as of April 2017, and a new amortization period for these costs will be determined in a future regulatory rate review. Costs incurred from August 2012 through December 2012 are being amortized over a six-year period that began in June 2015.


(o)	The period of recovery will depend on the timing of actual expenditures.


(p)	The MoPSC’s May 2010 electric rate order allowed Ameren Missouri to record an allowance for funds used during construction for pollution control equipment at its Sioux energy center until the cost of that equipment was included in customer rates beginning in 2011. These costs are being amortized over the expected life of the Sioux energy center, currently through 2033.


(q)	Costs associated with Ameren Missouri’s solar rebate program to fulfill its renewable energy requirements. Costs incurred from 2010 to 2014 are being amortized over a two-year period that began in April 2017 as modified per the MoPSC’s March 2017 electric rate order. Costs incurred from 2015 to 2016 are being amortized over a three-year period that began in April 2017.

(r)

Electric energy-efficiency program investment deferrals which earn a return at Ameren Illinois’ weighted-average cost of capital with the equity return based on the annual average of the monthly yields of the 30-year United States Treasury bonds plus 580 basis points. The investments are being amortized over their weighted-average useful lives beginning in the period in which they were made, with current remaining amortization periods ranging from 8 to 12 years.

(s)

The Ameren Missouri balance relates to the MEEIA. The MEEIA rider allows Ameren Missouri to collect from, or refund to, customers any annual difference in the actual amounts incurred and the amounts collected from customers for the MEEIA program costs, lost electric margins, and the performance incentive. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs, and lost electric margins are incurred or any performance incentive are earned. The Ameren Illinois balance relates to a regulatory tracking mechanism to recover its electric pre-FEJA costs and natural gas costs associated with developing, implementing, and evaluating customer energy efficiency and demand response programs. Any under-recovery or over-recovery will be collected from, or refunded to, customers over the year following the plan year.


(t)	Estimated refunds to transmission customers related to the February 2015 FERC complaint case discussed above.


(u)	Estimated funds collected for the eventual dismantling and removal of plant retired from service, net of salvage value.


(v)	Recoverable or refundable removal costs for AROs, including net realized and unrealized gains and losses related to the nuclear decommissioning trust fund investments. See Note 1 – Summary of Significant Accounting Policies – Asset Retirement Obligations.

(w)

A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri and the level of such costs included in customer rates. For costs incurred prior to August 2012, the amounts are being amortized over a two-year period that began in April 2017 as modified per the MoPSC’s March 2017 electric rate order. For costs incurred between August 2012 and December 2014, the MoPSC’s May 2015 electric rate order directed the amortization period to occur over a five-year period that began in June 2015. For costs incurred between January 2015 and December 2016, the MoPSC’s March 2017 electric rate order directed the amortization period to occur over a five-year period that began in April 2017. For costs incurred after December 2016, the amortization period will be determined in a future electric regulatory rate review.


(x)	Funds collected for the purchase of renewable energy credits and zero emission credits through IPA procurements. The balance will be amortized as the credits are purchased.


(y)	The excess amount collected in rates related to the TCJA from January 1, 2018, through July 31, 2018. The regulatory liability will be reflected in customer rates over a period of time to be determined by the MoPSC in the next regulatory rate review.