RATE AND REGULATORY MATTERS

Below is a summary of significant regulatory proceedings and related lawsuits. We are unable to predict the ultimate outcome of these matters, the timing of the final decisions of the various agencies and courts, or the effect on our results of operations, financial position, or liquidity.

Missouri

2015 Electric Rate Order

In April 2015, the MoPSC issued an order approving a $122 million increase in Ameren Missouri’s annual revenues for electric service, including $109 million related to the increase in net energy costs above those included in base rates previously authorized by the MoPSC. The revenue increase was based on a 9.53% return on common equity, a capital structure composed of 51.8% common equity, and a rate base of $7.0 billion to reflect investments through December 31, 2014. Rate changes consistent with the order became effective on May 30, 2015.

The order approved Ameren Missouri’s request for continued use of the FAC; however, it changed the FAC to exclude all transmission revenues and substantially all transmission charges. The order did not approve the continued use of the regulatory tracking mechanisms for storm costs or for vegetation management and infrastructure inspection costs. These changes to Ameren Missouri’s recovery mechanisms are expected to contribute to regulatory lag. The order did approve the continued use of the regulatory tracking mechanisms for pension and other postretirement benefits, renewable energy standard costs, solar rebates, and uncertain tax positions that the MoPSC authorized in prior electric rate orders.

In addition, the order approved a reduction to Noranda’s electric rates with an offsetting increase in electric rates for Ameren Missouri’s other customers. The rate shift is designed to be revenue neutral for Ameren Missouri. In June 2015, Ameren Missouri filed an appeal with the Missouri Court of Appeals, Western District, concerning the reduction to Noranda’s electric rates included in the MoPSC’s order. In February 2016, Ameren Missouri withdrew its appeal.

MEEIA

The MEEIA established a regulatory framework that, among other things, requires the MoPSC to ensure that a utility’s financial incentives are aligned to help customers use energy more efficiently, to provide timely cost recovery, and to provide earnings opportunities associated with cost-effective energy efficiency programs. Missouri does not have a law mandating energy efficiency programs.

In August 2012, the MoPSC approved Ameren Missouri’s customer energy efficiency programs, net shared benefits, and performance incentive for 2013 through 2015. From 2013 through 2015, Ameren Missouri invested $134 million in customer energy efficiency programs and realized $174 million of net shared benefits. The MoPSC also established a performance incentive that would provide Ameren Missouri an opportunity to earn additional revenues by achieving certain customer energy efficiency goals, including $19 million if 100% of the goals were achieved during the three-year period, with the potential to earn a larger performance incentive if Ameren Missouri’s energy savings exceeded those goals.

In June 2015, the MoPSC staff filed a complaint case with the MoPSC regarding the method and inputs used in calculating the performance incentive for 2014 and 2015. In November 2015, the MoPSC issued an order that adopted the MoPSC staff’s method and inputs used in calculating the performance incentive for 2014 and 2015. Ameren Missouri filed an appeal of the order with the Missouri Court of Appeals, Western District. If the Missouri Court of Appeals upholds the MoPSC order, the performance incentive awarded from the 2014 and 2015 MEEIA programs will be significantly less than the performance incentive calculated using Ameren Missouri’s interpretation. Ameren Missouri has not recorded revenues associated with the performance incentive for any of the MEEIA program years. Ameren Missouri believes that it will ultimately be found to have exceeded 100% of the customer energy efficiency goals, and it therefore expects to recognize revenues of at least $19 million in 2016.

In February 2016, the MoPSC issued an order approving Ameren Missouri's March 2016 to February 2019 MEEIA plan which included a portfolio of customer energy efficiency programs along with a rider to collect the program costs, the throughput disincentive, and a performance incentive from customers. The throughput disincentive recovery will replace the net shared benefits that were collected under the 2013 through 2015 MEEIA plan. The MEEIA rider will allow Ameren Missouri to collect the throughput disincentive without a traditional rate proceeding, until such time as lower volumes resulting from the MEEIA programs are reflected in base rates. Customer rates will be based upon both forecasted program costs and throughput disincentive which will be annually reconciled to actual results. Beginning in March 2016, Ameren Missouri intends to invest $158 million over the three-year period in customer energy efficiency programs. In addition, similar to the MEEIA plan that ended in December 2015, the MoPSC's order approved a performance incentive that would provide Ameren Missouri an opportunity to earn additional revenues by achieving certain customer energy efficiency goals, including $27 million if 100% of the goals are achieved during the three-year period, with the potential to earn more if Ameren Missouri's energy savings exceed those goals. Ameren Missouri must achieve at least 25% of its energy efficiency goals before it earns a performance incentive.

Noranda

Ameren Missouri supplies electricity to Noranda’s aluminum smelter located in southeast Missouri under a long-term power supply agreement. In May 2015, Ameren Missouri notified Noranda of its intent to terminate the agreement effective June 1, 2020. If Ameren Missouri wants to cease providing electricity to Noranda following the termination date, Ameren Missouri would also be required to obtain approval from the MoPSC.

On January 8, 2016, Noranda announced that production had been idled at two of its three pot lines at the smelter following an electric supply circuit failure on assets not owned by Ameren Missouri. On January 13, 2016, Noranda announced that the smelter’s “remaining operations will be curtailed on or before March 12, 2016, unless [Noranda] is able to secure a substantially more sustainable power rate for the smelter and materially improve [Noranda’s] overall liquidity.” Ameren Missouri has been working with Noranda, legislators and other stakeholders on a potential legislative solution to support Noranda’s operations.

In its April 2015 electric rate order, the MoPSC approved a rate design that established $78 million in annual revenues, net of fuel and purchased power costs, as Noranda’s portion of Ameren Missouri’s revenue requirement. The portion of Ameren Missouri’s annual revenue requirement reflected in Noranda’s electric rate is based on the smelter using approximately 4.2 million megawatthours annually, which is almost 100% of its operating capacity. Ameren Missouri’s rates, including those for Noranda, are seasonal. Noranda’s summer base rate (June through September) is $45.78 per megawatthour and its winter base rate (October through May) is $31.11 per megawatthour.

In 2016, actual sales volumes to Noranda will be significantly below the sales volumes reflected in rates. As a result, Ameren Missouri will not fully recover its revenue requirement until rates are adjusted by the MoPSC in a future electric rate case to accurately reflect Noranda’s actual sales volumes. In light of the Noranda announcements described above, Ameren Missouri expects to employ a provision in its FAC tariff that, under certain circumstances, allows Ameren Missouri to retain a portion of the revenues from any off-system sales it makes as a result of reduced tariff sales to Noranda. The current market price of electricity is less than Noranda’s electric rate, and Ameren Missouri expects market prices to remain below Noranda’s electric rate during 2016. Accordingly, this FAC provision would not enable Ameren Missouri to fully recover its revenue requirement under current market conditions.

Although Ameren Missouri has not decided when to file its next electric rate case, on January 11, 2016, Ameren Missouri filed a notice with the MoPSC, that would enable Ameren Missouri to file a rate case after 60 days. Ameren Missouri expects to file a rate case in 2016 and expects the resulting new rates to reflect Noranda’s actual sales volumes which would prospectively eliminate the impact of the current revenue shortfall. The rate case would take place over a period of up to 11 months from the date of filing. Ameren Missouri may seek recovery of lost revenues in a filing with the MoPSC for certain costs incurred but not contemporaneously recovered as a result of Noranda's reduced operations. Ameren Missouri will continue to monitor Noranda’s sales volumes and to evaluate regulatory and legislative options that might mitigate adverse financial impacts. The reduction in Noranda’s sales volumes will adversely affect Ameren’s and Ameren Missouri’s results of operations, financial condition, and liquidity until customer rates are adjusted in a future rate case.

On February 8, 2016, Noranda filed voluntary petitions for a court-supervised restructuring process under Chapter 11 of the United States Bankruptcy Code. In the filing, Noranda reaffirmed that the remaining pot line will continue to operate at the smelter until March 2016, at which time operation of the line will be curtailed. Noranda stated it would maintain the flexibility to restart operations at the smelter should conditions allow. For utility service through February 8, 2016, Noranda had prepaid an amount to Ameren Missouri in excess of its utility service usage. Ameren Missouri expects to be paid in full for utility services provided after February 8, 2016.

ATXI Transmission Projects

In May 2015, the MoPSC granted ATXI a certificate of convenience and necessity for the seven-mile portion of the Illinois Rivers project located in Missouri.

In June 2015, ATXI made a filing with the MoPSC requesting a certificate of convenience and necessity for the Mark Twain project. The Mark Twain project is a MISO-approved 100-mile transmission line located in northeast Missouri. A decision is expected from the MoPSC in 2016.

Illinois

IEIMA

Under the provisions of the IEIMA's performance-based formula rate-making framework, which currently extends through 2019, Ameren Illinois’ electric delivery service rates are subject to an annual revenue requirement reconciliation to its actual recoverable costs. Throughout each year, Ameren Illinois records a regulatory asset or a regulatory liability and a corresponding increase or decrease to operating revenues for any differences between the revenue requirement reflected in customer rates for that year and its estimate of the probable increase or decrease in the revenue requirement expected to ultimately be approved by the ICC based on that year's actual recoverable costs incurred. As of December 31, 2015, Ameren Illinois had recorded regulatory assets of $62 million and $103 million, including interest, to reflect its expected 2015 and the 2014 approved revenue requirement reconciliation adjustments, respectively. As of December 31, 2014, Ameren Illinois had recorded a $65 million regulatory asset to reflect its approved 2013 revenue requirement reconciliation adjustment, which was collected, with interest, from customers during 2015.

In December 2015, the ICC issued an order in Ameren Illinois’ annual update filing approving a $106 million increase in Ameren Illinois’ electric delivery service revenue requirement beginning in January 2016. This update reflects an increase to the annual formula rate based on 2014 actual recoverable costs and expected net plant additions for 2015, an increase to include the 2014 revenue requirement reconciliation adjustment, which was recorded as a regulatory asset at December 31, 2015, and a decrease for the conclusion of the 2013 revenue requirement reconciliation adjustment, which was fully collected from customers in 2015.

In December 2013, the ICC issued an order that disallowed, in part, the recovery from customers of the debt premium costs paid by Ameren Illinois for a tender offer in August 2012 to repurchase outstanding senior secured notes. As a result of the ICC order, in 2013, Ameren and Ameren Illinois each recorded a pretax charge to earnings of $15 million relating to the partial disallowance of the debt premium costs. In December 2014, the ICC issued an order that allowed partial recovery from customers of the previously disallowed debt premium costs. Accordingly, in 2014, Ameren and Ameren Illinois each recorded a pretax increase to earnings of $11 million to reflect the partial recovery of the debt premium costs. Ameren and Ameren Illinois recorded the effects of the 2013 and 2014 orders to "Interest charges" with a corresponding offset to "Regulatory assets."

2015 Natural Gas Delivery Service Rate Order

In December 2015, the ICC issued a rate order that approved an increase in revenues for Ameren Illinois' natural gas delivery service of $45 million. The revenue increase was based on a 9.6% return on common equity, a capital structure composed of 50% common equity, and a rate base of $1.2 billion. The rate order was based on a 2016 future test year. The rate changes were in effect in January 2016. In addition, the rate order approved the VBA for residential and small nonresidential customers beginning in 2016.

2015 ICC Purchased Power Reconciliation

In January 2015, the ICC issued an order that approved Ameren Illinois' reconciliation of revenues collected under its purchased power rider mechanism and Ameren Illinois' related cumulative power usage cost. In the first quarter of 2015, based on the January 2015 order, both Ameren and Ameren Illinois recorded a $15 million increase to electric revenues for the recovery of this cumulative power usage cost from electric customers.

ATXI Transmission Project

The Spoon River project is a MISO-approved 46-mile transmission line to be constructed in northwest Illinois. In September 2015, the ICC granted a certificate of public convenience and necessity and project approval for the Spoon River project.

Federal

Ameren Illinois Electric Transmission Rate Refund

In July 2012, the FERC issued an order concluding that Ameren Illinois improperly included acquisition premiums, including goodwill, in determining the common equity used in its electric transmission formula rate and thereby inappropriately recovered a higher amount from its electric transmission customers. The order required Ameren Illinois to make refunds to customers for such improperly included amounts.

In July 2015, the FERC approved a settlement agreement between Ameren Illinois and the affected customers. The settlement agreement required Ameren Illinois to make refunds and payments of $8 million to electric transmission customers, all of which was paid in 2015. The settlement agreement also required Ameren Illinois to take other actions, such as reducing common equity for electric transmission ratemaking purposes on a prospective basis. The transmission rates that became effective on January 1, 2016, reflect these adjustments.

FERC Complaint Cases

In November 2013, a customer group filed a complaint case with the FERC seeking a reduction in the allowed base return on common equity for the FERC-regulated transmission rate base under the MISO tariff from 12.38% to 9.15%. In December 2015, an administrative law judge issued an initial decision in the November 2013 complaint case that would lower the allowed base return on common equity to 10.32% and would require customer refunds to be issued for the 15-month period ending February 2015. The allowed base return on common equity in the initial decision was based on multiple inputs, including observable market data for the six months ended June 30, 2015. The FERC is expected to issue a final order on the November 2013 complaint case by October 2016.

As the maximum FERC-allowed refund period for the November 2013 complaint case ended in February 2015, another customer complaint case was filed in February 2015. The February 2015 complaint case seeks a reduction in the allowed base return on common equity for the FERC-regulated transmission rate base under the MISO tariff to 8.67%. The initial decision from an administrative law judge in the February 2015 complaint case, which will subsequently require FERC approval, is expected to be issued by June 2016.

On January 6, 2015, a FERC-approved incentive adder of up to 50 basis points on the allowed base return on common equity for our participation in an RTO became effective. Beginning with its January 6, 2015 effective date, the incentive adder will reduce any refund to customers relating to a reduction of the allowed base return on common equity from the complaint cases discussed above.

As of December 31, 2015, Ameren and Ameren Illinois had current regulatory liabilities of $45 million and $32 million, respectively, representing their estimates of the potential refunds from the November 12, 2013 refund effective date through December 31, 2015. Ameren and Ameren Illinois recorded liabilities to reflect the allowed base return on common equity in the initial decision for the November 2013 complaint case refund period, and the observable market data for the six months ended December 31, 2015, for the February 2015 complaint case refund period. Ameren’s and Ameren Illinois’ liabilities also reflect the January 6, 2015 incentive adder discussed above. Ameren Missouri did not record a liability as of December 31, 2015, and it does not expect that a reduction in the FERC-allowed base return on common equity for MISO transmission owners would be material to its results of operations, financial position, or liquidity.

Combined Construction and Operating License

In 2008, Ameren Missouri filed an application with the NRC for a COL for a second nuclear unit at Ameren Missouri's existing Callaway County, Missouri, energy center site. In 2009, Ameren Missouri suspended its efforts to build a second nuclear unit at its existing Callaway site, and the NRC suspended review of the COL application. Prior to suspending its efforts, Ameren Missouri had capitalized $69 million related to the project. Primarily because of changes in vendor support for licensing efforts at the NRC, Ameren Missouri’s assessment of long-term capacity needs, declining costs of alternative generation technologies, and the regulatory framework in Missouri, Ameren Missouri discontinued its efforts to license and build a second nuclear unit at its existing Callaway site. As a result of this decision, in the second quarter of 2015, Ameren and Ameren Missouri recognized a $69 million noncash pretax provision for all of the previously capitalized COL costs. Ameren Missouri has withdrawn its COL application with the NRC.

Regulatory Assets and Liabilities

In accordance with authoritative accounting guidance regarding accounting for the effects of certain types of regulation, we defer certain costs as regulatory assets pursuant to actions of regulators or because we expect to recover such costs in rates charged to customers. We may also defer certain amounts as regulatory liabilities because of actions of regulators or because we expect that such amounts will be returned to customers in future rates. The following table presents our regulatory assets and regulatory liabilities at December 31, 2015 and 2014:



	2015						2014
	Ameren Missouri		Ameren Illinois		Ameren			Ameren Missouri		Ameren Illinois		Ameren
Current regulatory assets:
Under-recovered FAC^(a)(b)	$	37	$	—	$	37		$	128	$	—	$	128
Under-recovered Illinois electric power costs^(c)	—		3		3			—		2		2
Under-recovered PGA^(c)	—		8		8			—		20		20
MTM derivative losses^(d)	29		45		74			32		42		74
Energy efficiency riders^(e)	23		—		23			3		—		3
IEIMA revenue requirement reconciliation adjustment^(a)(f)	—		103		103			—		65		65
FERC revenue requirement reconciliation adjustment^(a)(g)	—		8		12			—		—		3
Total current regulatory assets	$	89	$	167	$	260		$	163	$	129	$	295
Noncurrent regulatory assets:
Pension and postretirement benefit costs^(h)	$	95	$	202	$	297		$	148	$	275	$	423
Income taxes⁽ⁱ⁾	254		4		258			253		3		256
Asset retirement obligations^(j)	—		4		4			—		5		5
Callaway costs^(a)(k)	32		—		32			36		—		36
Unamortized loss on reacquired debt^(a)(l)	69		69		138			72		80		152
Contaminated facilities costs^(m)	—		230		230			—		251		251
MTM derivative losses^(d)	15		175		190			14		144		158
Storm costs^(a)(n)	—		9		9			—		3		3
Demand-side costs before the MEEIA implementation^(a)(o)	31		—		31			44		—		44
Workers’ compensation claims^(p)	6		7		13			7		7		14
Credit facilities fees^(q)	4		—		4			5		—		5
Construction accounting for pollution control equipment^(a)(r)	20		—		20			21		—		21
Solar rebate program^(a)(s)	74		—		74			88		—		88
IEIMA revenue requirement reconciliation adjustment^(a)(f)	—		62		62			—		101		101
FERC revenue requirement reconciliation adjustment^(a)(g)	—		5		11			—		8		12
Other	5		4		9			7		6		13
Total noncurrent regulatory assets	$	605	$	771	$	1,382		$	695	$	883	$	1,582
Current regulatory liabilities:
Over-recovered FAC^(b)	$	9	$	—	$	9		$	—	$	—	$	—
Over-recovered Illinois electric power costs^(c)	—		6		6			—		26		26
Over-recovered PGA^(c)	3		—		3			2		25		27
MTM derivative gains^(d)	16		1		17			16		1		17
FERC revenue requirement reconciliation adjustment^(g)	—		—		—			—		11		11
Estimated refund for FERC complaint cases, orders, and audit findings^(t)	—		32		45			—		21		25
Total current regulatory liabilities	$	28	$	39	$	80		$	18	$	84	$	106
Noncurrent regulatory liabilities:
Income taxes^(u)	$	36	$	6	$	42		$	41	$	14	$	55
Uncertain tax positions tracker^(v)	6		—		6			7		—		7
Removal costs^(w)	933		671		1,605			886		643		1,529
Asset retirement obligation^(j)	167		—		167			182		—		182
Bad debt riders^(x)	—		6		6			—		7		7
Pension and postretirement benefit costs tracker^(y)	19		—		19			24		—		24
Energy efficiency riders^(e)	—		36		36			—		39		39
Renewable energy credits^(z)	—		12		12			1		—		1
Storm tracker^(aa)	9		—		9			6		—		6
Other	2		1		3			—		—		—
Total noncurrent regulatory liabilities	$	1,172	$	732	$	1,905		$	1,147	$	703	$	1,850


(a)	These assets earn a return.


(b)	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.


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


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

(e)

The Ameren Missouri balance relates to the MEEIA. Beginning in January 2014, the MEEIA rider allowed 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 and its net shared benefits. Under the MEEIA rider, collections from or refunds to customers occur one year after the program costs and lost revenues are incurred. The Ameren Illinois balance relates to a regulatory tracking mechanism to recover its electric 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 12 months following the plan year.


(f)	The difference between Ameren Illinois' annual revenue requirement calculated under the IEIMA's performance-based formula ratemaking framework and the revenue requirement included in customer rates for that year. Subject to ICC approval, these amounts will be collected from or refunded to customers with interest within two years.


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


(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 11 – Retirement Benefits for additional information.


(i)	Tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate changes. This will be recovered over the expected life of the related assets.


(j)	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 and Investments.


(k)	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 remaining life of the energy center's original operating license through 2024.


(l)	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.


(m)	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 15 – Commitments and Contingencies for additional information.


(n)	Storm costs from 2013 and 2015 deferred in accordance with the IEIMA. These costs are being amortized over five-year periods beginning in 2013 and 2015, respectively.

(o)

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. Costs incurred from May 2008 through September 2008 are being amortized over a 10-year period that began in March 2009. Costs incurred from October 2008 through December 2009 are being amortized until May 2017. Costs incurred from January 2010 through February 2011 are being amortized over a six-year period that began in August 2011. Costs incurred from March 2011 through July 2012 are being amortized over a six-year period that began in January 2013. Costs incurred from August 2012 through December 2012 are being amortized over a six-year period that began in June 2015.


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


(q)	Ameren Missouri’s costs incurred to enter into and maintain the Missouri Credit Agreement. Additional costs were incurred in December 2014 to amend and restate the Missouri Credit Agreement. These costs are being amortized over the life of the credit facility, ending in December 2019, to construction work in progress, which will be depreciated when assets are placed into service.


(r)	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, which is currently through 2033.


(s)	Costs associated with Ameren Missouri's solar rebate program beginning in August 2012 to fulfill its renewable energy portfolio requirement. These costs are being amortized over three years, beginning in June 2015.


(t)	Estimated refunds to transmission customers related to FERC orders. See Ameren Illinois Electric Transmission Rate Refund and FERC Complaint Cases above.


(u)	Unamortized portion of investment tax credits and reductions to deferred tax liabilities recorded at rates in excess of current statutory rates. The unamortized portion of investment tax credits and the reduction to deferred tax liabilities are being amortized over the expected life of the underlying assets.


(v)	The tracker is amortized over three years, beginning from the date the amounts are included in rates. See Note 13 – Income Taxes for additional information.


(w)	Estimated funds collected for the eventual dismantling and removal of plant from service, net of salvage value, upon retirement related to our rate-regulated operations.

(x)

A regulatory tracking mechanism for the difference between the level of bad debt incurred by Ameren Illinois under GAAP and the level of such costs included in electric and natural gas rates. The over-recovery relating to 2013 was refunded to customers from June 2014 through May 2015. The over-recovery relating to 2014 will be refunded to customers from June 2015 through May 2016. The over-recovery relating to 2015 will be refunded to customers from June 2016 through May 2017.

(y)

A regulatory tracking mechanism for the difference between the level of pension and postretirement benefit costs incurred by Ameren Missouri under GAAP and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over three to five years, beginning in June 2015. For periods after December 2014, the amortization period will be determined in a future electric rate case.

(z)

The Ameren Missouri balance includes the costs of renewable energy credits to fulfill Ameren Missouri's renewable energy portfolio requirement from August 2012 through December 2013, which were less than the amount included in rates. These costs are being amortized over three years beginning in June 2015. The Ameren Illinois balance includes funds collected from customers for the purchase of renewable energy credits through IPA procurements for distributed generation. The balance will be amortized as renewable energy credits are purchased.

(aa)

A regulatory tracking mechanism at Ameren Missouri for the difference between the level of storm costs incurred in a particular year and the level of such costs included in rates. For periods prior to December 2014, the MoPSC's April 2015 electric rate order directed the amortization to occur over five years, beginning in June 2015. For periods after December 2014, the amortization period will be determined in a future electric rate case. The April 2015 MoPSC order did not approve the continued use of the regulatory tracking mechanisms for storm costs.

Ameren, Ameren Missouri, and Ameren Illinois continually assess the recoverability of their regulatory assets. Under current accounting standards, regulatory assets are charged to earnings when it is no longer probable that such amounts will be recovered through future revenues. To the extent that payments of regulatory liabilities are no longer probable, the amounts are credited to earnings.