SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

General

Ameren, headquartered in St. Louis, Missouri, is a public utility holding company whose primary assets are its equity interests in its subsidiaries. Ameren’s subsidiaries are separate, independent legal entities with separate businesses, assets, and liabilities. Dividends on Ameren’s common stock and the payment of expenses by Ameren depend on distributions made to it by its subsidiaries. Ameren’s principal subsidiaries are listed below. Ameren also has other subsidiaries that conduct other activities, such as providing shared services.

•

Union Electric Company, doing business as Ameren Missouri, operates a rate-regulated electric generation, transmission, and distribution business and a rate-regulated natural gas distribution business in Missouri. Ameren Missouri was incorporated in Missouri in 1922 and is successor to a number of companies, the oldest of which was organized in 1881. It is the largest electric utility in the state of Missouri. It supplies electric and natural gas service to a 24,000-square-mile area in central and eastern Missouri, which includes the Greater St. Louis area. Ameren Missouri supplies electric service to 1.2 million customers and natural gas service to 0.1 million customers.

•

Ameren Illinois Company, doing business as Ameren Illinois, operates rate-regulated electric transmission, electric distribution, and natural gas distribution businesses in Illinois. Ameren Illinois was incorporated in Illinois in 1923 and is the successor to a number of companies, the oldest of which was organized in 1902. Ameren Illinois supplies electric and natural gas utility service to a 40,000 square mile area in central and southern Illinois. Ameren Illinois supplies electric service to 1.2 million customers and natural gas service to 0.8 million customers.

•

Ameren Transmission Company of Illinois, doing business as ATXI, operates a FERC rate-regulated electric transmission business. ATXI was incorporated in Illinois in 2006. ATXI is constructing MISO-approved electric transmission projects, including the Illinois Rivers and Mark Twain projects, and operates the Spoon River project, which was placed in service in February 2018. Ameren also evaluates competitive electric transmission investment opportunities as they arise.

Ameren’s financial statements are prepared on a consolidated basis and therefore include the accounts of its majority-owned subsidiaries. All intercompany transactions have been eliminated. Ameren Missouri and Ameren Illinois have no subsidiaries. All tabular dollar amounts are in millions, unless otherwise indicated.

Our accounting policies conform to GAAP. Our financial statements reflect all adjustments (which include normal, recurring adjustments) that are necessary, in our opinion, for a fair presentation of our results. The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions. Such estimates and assumptions affect reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the dates of financial statements, and the reported amounts of revenues and expenses during the reported periods. Actual results could differ from those estimates.

Regulation

We are regulated by the MoPSC, the ICC, and the FERC. We defer certain costs as assets pursuant to actions of rate regulators or because of expectations that we will be able to recover such costs in future rates charged to customers. We also defer certain amounts as liabilities pursuant to actions of rate regulators or based on the expectation that such amounts will be returned to customers in future rates. Regulatory assets and liabilities are amortized consistent with the period of expected regulatory treatment. Ameren Missouri and Ameren Illinois have various rate-adjustment mechanisms in place that provide for the recovery of purchased natural gas and electric fuel and purchased power costs without a traditional regulatory rate review.

In Ameren Missouri’s and Ameren Illinois’ natural gas businesses, changes in natural gas costs are reflected in billings to their respective customers through PGA clauses. The difference between actual natural gas costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period.

Ameren Missouri has a FAC that allows an adjustment of electric rates three times per year, without a traditional rate proceeding, for a pass-through to customers of 95% of the variance in net energy costs from the amount set in base rates, subject to MoPSC prudence review. The difference between the actual amounts incurred for these items and the amounts recovered from Ameren Missouri customers’ base rates is deferred as a regulatory asset or liability. The deferred amounts are either billed or refunded to customers in a subsequent period.

In Ameren Illinois’ electric distribution business, changes in purchased power and transmission service costs are reflected in billings to its customers through pass-through rate-adjustment clauses. The difference between actual purchased power and transmission service costs and costs billed to customers in a given period is deferred as a regulatory asset or liability. The deferred amount is either billed or refunded to customers in a subsequent period.

In addition to the rate-adjustment mechanisms discussed above, Ameren Missouri and Ameren Illinois have approvals from rate regulators to use other cost recovery mechanisms. Ameren Missouri has a pension and postretirement benefit cost tracker, an uncertain tax position tracker, a tracker on certain excess deferred taxes, a renewable energy standards cost tracker, a solar rebate program tracker, PISA, and a RESRAM. Ameren Illinois’ and ATXI’s electric transmission rates are determined pursuant to formula ratemaking. Ameren Illinois participates in performance-based formula ratemaking for its electric distribution business and its electric energy-efficiency investments. Ameren Illinois also has environmental cost riders, an asbestos-related litigation rider, a natural gas energy-efficiency rider, a QIP rider, a VBA rider, a bad debt rider, and cost recovery mechanisms for renewable energy credits and zero emission credits. See Note 2 – Rate and Regulatory Matters for additional information on the regulatory assets and liabilities recorded at December 31, 2018 and 2017.

Ameren, Ameren Missouri, and Ameren Illinois continually assess the recoverability of their regulatory assets. 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 reductions in customers rates or refunds to customers related to regulatory liabilities are no longer probable, the amounts are credited to earnings.

Cash, Cash Equivalents, and Restricted Cash

Cash and cash equivalents include short-term, highly liquid investments purchased with an original maturity of three months or less. Cash and cash equivalents subject to legal or contractual restrictions and not readily available for use for general corporate purposes are classified as restricted cash.

In November 2016, the FASB issued authoritative guidance that requires, including on a retrospective basis, restricted cash to be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. Our adoption of this guidance, effective January 2018, did not result in material changes to previously reported cash flows from operating, investing, or financing activities. The changes in our restricted cash balances during the year ended December 31, 2018, were primarily reflected as increases in cash provided by operating activities as a result of our adoption of this guidance.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets as of December 31, 2018 and 2017:



	December 31, 2018						December 31, 2017
	Ameren		Ameren Missouri		Ameren Illinois		Ameren		Ameren Missouri		Ameren Illinois
Cash and cash equivalents	$	16	$	—	$	—	$	10	$	—	$	—
Restricted cash included in “Other current assets”	13		4		6		21		5		6
Restricted cash included in “Other assets”	74		—		74		35		—		35
Restricted cash included in “Nuclear decommissioning trust fund”	4		4		—		2		2		—
Total cash, cash equivalents, and restricted cash	$	107	$	8	$	80	$	68	$	7	$	41

Restricted cash included in Ameren’s other current assets primarily represents participant funds from Ameren (parent)’s DRPlus and funds held by an irrevocable Voluntary Employee Beneficiary Association (VEBA) trust, which provides health care benefits for active employees. Restricted cash included in Ameren Missouri’s and Ameren Illinois’ other current assets primarily represents funds held by the VEBA trust.

Restricted cash included in Ameren’s and Ameren Illinois’ other assets primarily represents amounts in a trust fund restricted for the use of funding certain asbestos-related claims and amounts collected under a cost recovery rider that are restricted for use in the procurement of renewable energy credits.

Accounts Receivable

“Accounts receivable – trade” on Ameren’s and Ameren Illinois’ balance sheets include certain receivables purchased at a discount from alternative retail electric suppliers that elect to participate in the utility consolidated billing program. At December 31, 2018 and 2017, “Other current liabilities” on Ameren’s and Ameren Illinois’ balance sheets included payables for purchased receivables of $33 million and $31 million, respectively.

For the years ended December 31, 2018, 2017, and 2016 the Ameren Companies recorded immaterial bad debt expense.

Allowance for Doubtful Accounts Receivable

The allowance for doubtful accounts represents our estimate of existing accounts receivable that will ultimately be uncollectible. The allowance is calculated by applying estimated loss factors to various classes of outstanding receivables, including unbilled revenue. The loss factors used to estimate uncollectible accounts are based upon both historical collections experience and management’s estimate of future collections success given the existing and anticipated future collections environment. Ameren Illinois has a bad debt rider that adjusts rates for net write-offs of customer accounts receivable above or below those being collected in rates.

Inventories

Inventories are recorded at the lower of weighted-average cost or net realizable value. Inventories are capitalized when purchased and then expensed as consumed or capitalized as property, plant, and equipment when installed, as appropriate. The following table presents a breakdown of inventories for each of the Ameren Companies at December 31, 2018 and 2017:



	Ameren Missouri		Ameren Illinois		Ameren
2018
Fuel^(a)	$	123	$	—	$	123
Natural gas stored underground	7		64		71
Materials, supplies, and other	228		61		289
Total inventories	$	358	$	125	$	483
2017
Fuel^(a)	$	154	$	—	$	154
Natural gas stored underground	8		74		82
Materials, supplies, and other	226		60		286
Total inventories	$	388	$	134	$	522


(a)	Consists of coal, oil, and propane.

Property, Plant, and Equipment, Net

We capitalize the cost of additions to, and betterments of, units of property, plant, and equipment. The cost includes labor, material, applicable taxes, and overhead. An allowance for funds used during construction, as discussed below, is also capitalized as a cost of our rate-regulated assets. Maintenance expenditures, including nuclear refueling and maintenance outages, are expensed as incurred. When units of depreciable property are retired, the original costs, less salvage values, are charged to accumulated depreciation. If environmental expenditures are related to assets currently in use, as in the case of the installation of pollution control equipment, the cost is capitalized and depreciated over the expected life of the asset. See Asset Retirement Obligations section below and Note 3 – Property, Plant, and Equipment, Net for additional information.

Ameren Missouri’s cost of nuclear fuel is capitalized as a part of “Property, Plant, and Equipment, Net” on the balance sheet and then amortized to fuel expense on a unit-of-production basis. The cost is charged to “Operating Expenses – Fuel” in the statement of income.

Depreciation

Depreciation is provided over the estimated lives of the various classes of depreciable property by applying composite rates on a straight-line basis to the cost basis of such property. The provision for depreciation for the Ameren Companies in 2018, 2017, and 2016 ranged from 3% to 4% of the average depreciable cost. See Note 3 – Property, Plant, and Equipment, Net for additional information on estimated depreciable lives.

Allowance for Funds Used During Construction

We capitalize allowance for funds used during construction, or the cost of borrowed funds and the cost of equity funds (preferred and common shareholders’ equity) applicable to rate-regulated construction expenditures, in accordance with the utility industry’s accounting practice and GAAP. Allowance for funds used during construction does not represent a current source of cash funds. This accounting practice offsets the effect on earnings of the cost of financing during construction, and it treats such financing costs in the same manner as construction charges for labor and materials.

Under accepted ratemaking practice, cash recovery of allowance for funds used during construction and other construction costs occurs when completed projects are placed in service and reflected in customer rates. The following table presents the average allowance for funds used during construction debt and equity blended rates that were applied to construction projects in 2018, 2017, and 2016:



	2018		2017		2016
Ameren Missouri	7	%	7	%	7	%
Ameren Illinois	5	%	4	%	5	%

Goodwill

Goodwill represents the excess of the purchase price of an acquisition over the fair value of the net assets acquired. Ameren and Ameren Illinois had goodwill of $411 million at December 31, 2018 and 2017. Ameren has four reporting units: Ameren Missouri, Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Transmission. Ameren Illinois has three reporting units: Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission. Ameren Illinois Electric Distribution, Ameren Illinois Natural Gas, and Ameren Illinois Transmission had goodwill of $238 million, $80 million, and $93 million, respectively, at December 31, 2018 and 2017. The Ameren Transmission reporting unit had the same $93 million of goodwill as the Ameren Illinois Transmission reporting unit at December 31, 2018 and 2017.

Ameren and Ameren Illinois evaluate goodwill for impairment in each of their reporting units as of October 31 each year, or more frequently if events and circumstances change that would more likely than not reduce the fair value of their reporting units below their carrying amounts. To determine whether the fair value of a reporting unit is more likely than not greater than its carrying amount, Ameren and Ameren Illinois elect to perform either a qualitative assessment or to bypass the qualitative assessment and perform a quantitative test, on an annual basis.

Ameren and Ameren Illinois elected to perform a qualitative assessment for their annual goodwill impairment test conducted as of October 31, 2018. The results of Ameren’s and Ameren Illinois’ qualitative assessment indicated that it was more likely than not that the fair value of each reporting unit significantly exceeded its carrying value as of October 31, 2018, resulting in no impairment of Ameren’s or Ameren Illinois’ goodwill. The following factors, among others, were considered by Ameren and Ameren Illinois when they assessed whether it was more likely than not that the fair value of each of their reporting units exceeded its carrying value as of October 31, 2018:


•	macroeconomic conditions, including those conditions within Ameren Illinois’ service territory;


•	pending regulatory rate review outcomes and projections of future regulatory rate review outcomes;


•	changes in laws and potential law changes;


•	observable industry market multiples;


•	achievement of IEIMA and FEJA performance metrics and the yield of the 30-year United States Treasury bonds;


•	changes in the FERC-allowed return on equity with respect to transmission services; and


•	projected operating results and cash flows.

Impairment of Long-lived Assets

We evaluate long-lived assets classified as held and used for impairment when events or changes in circumstances indicate that the carrying value of such assets may not be recoverable. Whether an impairment has occurred is determined by comparing the estimated undiscounted cash flows attributable to the assets to the carrying value of the assets. If the carrying value exceeds the undiscounted cash flows, we recognize an impairment charge equal to the amount by which the carrying value exceeds the estimated fair value of the assets. In the period in which we determine that an asset meets held for sale criteria, we record an impairment charge to the extent the book value exceeds its estimated fair value less cost to sell. We did not identify any events or changes in circumstances that indicated that the carrying value of long-lived assets may not be recoverable in 2018 and 2017.

Variable Interest Entities

As of December 31, 2018, Ameren and Ameren Missouri had interests in unconsolidated variable interest entities that were established to construct wind generation facilities and, ultimately, sell those constructed facilities to Ameren Missouri. Neither Ameren nor Ameren Missouri are the primary beneficiary of these variable interest entities because neither has the power to direct matters that most significantly affect the entities' activities, which include designing, financing, and constructing the wind generation facilities. As a result, these variable interest entities are not required to be consolidated. As of December 31, 2018, the maximum exposure to loss related to these variable interest entities was approximately $16 million, which represents the portion of interconnection study costs that may be incurred by Ameren and Ameren Missouri. The risk of a loss was assessed to be remote and, accordingly, Ameren and Ameren Missouri have not recognized a liability associated with any portion of the maximum exposure to loss. See Note 2 – Rate and Regulatory Matters for additional information on the agreements to acquire these wind generation facilities.

As of December 31, 2018 and 2017, Ameren also had investments in unconsolidated variable interest entities totaling $22 million and $17 million, respectively, included in “Other assets” on Ameren’s consolidated balance sheet. These investments are accounted for as equity method investments. Ameren is not the primary beneficiary of these variable interest entities because it does not have the power to direct matters that most significantly affect the entities' activities. As a result, these variable interest entities are not required to be consolidated. As of December 31, 2018, the maximum exposure to loss related to these variable interest entities is limited to the investment in these partnerships of $22 million plus associated outstanding funding commitments of $16 million.

Environmental Costs

Liabilities for environmental costs are recorded on an undiscounted basis when it is probable that a liability has been incurred and the amount of the liability can be reasonably estimated. Costs are expensed or deferred as a regulatory asset when it is expected that the costs will be recovered from customers in future rates.

Asset Retirement Obligations

We record the estimated fair value of legal obligations associated with the retirement of tangible long-lived assets in the period in which the liabilities are incurred and capitalize a corresponding amount as part of the book value of the related long-lived asset. In subsequent periods, we adjust AROs based on changes in the estimated fair values of the obligations with a corresponding increase or decrease in the asset book value. Asset book values, reflected within “Property, Plant, and Equipment, Net” on the balance sheet, are depreciated over the remaining useful life of the related asset. Due to regulatory recovery, that depreciation is deferred as a regulatory balance. The depreciation of the asset book values at Ameren Missouri was $14 million, $26 million, and $31 million for the years ended December 31, 2018, 2017, and 2016, respectively, which was deferred as a reduction to the net regulatory liability. The net regulatory liability also reflects deferrals of net realized and unrealized gains and losses within the nuclear decommissioning trust fund for the Callaway energy center. The depreciation deferred to the regulatory asset at Ameren Illinois was immaterial in each respective period. Uncertainties as to the probability, timing, or amount of cash expenditures associated with AROs affect our estimates of fair value. Ameren and Ameren Missouri have recorded AROs for retirement costs associated with Ameren Missouri’s Callaway energy center decommissioning, CCR facilities, and river structures. Also, Ameren, Ameren Missouri, and Ameren Illinois have recorded AROs for retirement costs associated with asbestos removal and the disposal of certain transformers. Asset removal costs that do not constitute legal obligations are classified as regulatory liabilities. See Note 2 – Rate and Regulatory Matters.

The following table provides a reconciliation of the beginning and ending carrying amount of AROs for the years ended December 31, 2018 and 2017:



	Ameren Missouri				Ameren Illinois				Ameren
Balance at December 31, 2016	$	644			$	6			$	650
Liabilities settled	(12		)		(1		)		(13		)
Accretion^(a)	26				—				26
Change in estimates^(b)	(18		)		(1		)		(19		)
Balance at December 31, 2017	$	640		^(c)	$	4		^(d)	$	644		^(c)
Liabilities settled	(7		)		—				(7		)
Accretion^(a)	27				—				27
Change in estimates^(e)	(14		)		—				(14		)
Balance at December 31, 2018	$	646		^(c)	$	4		^(d)	$	650		^(c)


(a)	Ameren Missouri’s accretion expense was deferred as a decrease to regulatory liabilities.


(b)	Ameren Missouri changed its fair value estimate primarily because of an extension of the remediation period of certain CCR storage facilities, an update to the decommissioning of the Callaway energy center to reflect the cost study and funding analysis filed with the MoPSC in 2017, and an increase in the assumed discount rate.


(c)	Balance included $23 million and $6 million in “Other current liabilities” on the balance sheet as of December 31, 2018 and 2017, respectively.


(d)	Included in “Other deferred credits and liabilities” on the balance sheet.


(e)	Ameren Missouri changed its fair value estimate primarily due to a reduction in the cost estimate for closure of certain CCR storage facilities.

Company-owned Life Insurance

Ameren and Ameren Illinois have company-owned life insurance, which is recorded at the net cash surrender value. The net cash surrender value is the amount that can be realized under the insurance policies at the balance sheet date. As of December 31, 2018, the cash surrender value of company-owned life insurance at Ameren and Ameren Illinois was $244 million (December 31, 2017 – $265 million) and $122 million (December 31, 2017 – $129 million), respectively, while total borrowings against the policies were $113 million (December 31, 2017 – $120 million) at both Ameren and Ameren Illinois. Ameren and Ameren Illinois have the right to offset the borrowings against the cash surrender value of the policies and, consequently, present the net asset in “Other assets” on their respective balance sheets.

Noncontrolling Interests

As of December 31, 2018 and 2017, Ameren’s noncontrolling interests included the preferred stock of Ameren Missouri and Ameren Illinois.

Operating Revenues

In the first quarter of 2018, we adopted authoritative accounting guidance related to revenue from contracts with customers using the full retrospective method, with no material changes to the amount or timing of revenue recognition. We record revenues from contracts with customers for various electric and natural gas services, which primarily consist of retail distribution, electric transmission, and off-system arrangements. When more than one performance obligation exists in a contract, the consideration under the contract is allocated to the performance obligations based on the relative standalone selling price.

Electric and natural gas retail distribution revenues are earned when the commodity is delivered to our customers. We accrue an estimate of electric and natural gas retail distribution revenues for service provided but unbilled at the end of each accounting period.

Electric transmission revenues are earned as electric transmission services are provided.

Off-system revenues are primarily comprised of MISO revenues and wholesale bilateral revenues. MISO revenues include the sale of electricity, capacity, and ancillary services. Wholesale bilateral revenues include the sale of electricity and capacity. MISO-related electricity and wholesale bilateral electricity revenues are earned as electricity is delivered. MISO-related capacity and ancillary service revenues and wholesale bilateral capacity revenues are earned as services are provided.

Retail distribution, electric transmission, and off-system revenues, including the underlying components described above, represent a series of goods or services that are substantially the same and have the same pattern of transfer over time to our customers. Revenues from contracts with customers are equal to the amounts billed and our estimate of electric and natural gas retail distribution services provided but unbilled at the end of each accounting period. Revenues are billed at least monthly, and payments are due less than one month after goods and/or services are provided. See Note 15 – Segment Information for disaggregated revenue information.

For certain regulatory recovery mechanisms that are alternative revenue programs rather than revenues from contracts with customers, we recognize revenues that have been authorized for rate recovery, are objectively determinable and probable of recovery, and are expected to be collected from customers within two years from the end of the year. Our alternative revenue programs include revenue requirement reconciliations, MEEIA, and VBA. These revenues are subsequently recognized as revenues from contracts with customers when billed, with an offset to alternative revenue program revenues.

The Ameren Companies elected not to disclose the aggregate amount of the transaction price allocated to the performance obligations that are unsatisfied as of the end of the reporting period for contracts with an initial expected term of one year or less. As of December 31, 2018 and 2017, our remaining performance obligations were immaterial.

Accounting for MISO Transactions

MISO-related purchase and sale transactions are recorded by Ameren, Ameren Missouri, and Ameren Illinois using settlement information provided by MISO. Ameren Missouri records these purchase and sale transactions on a net hourly position. Ameren Missouri records net purchases in a single hour in “Operating Expenses – Purchased power” and net sales in a single hour in “Operating Revenues – Electric” in its statement of income. Ameren Illinois records net purchases in “Operating Expenses – Purchased power” in its statement of income to reflect all of its MISO transactions relating to the procurement of power for its customers. On occasion, Ameren Missouri’s and Ameren Illinois’ prior-period transactions will be resettled outside the routine settlement process because of a change in MISO’s tariff or a material interpretation thereof. In these cases, Ameren Missouri and Ameren Illinois recognize expenses associated with resettlements once the resettlement is probable and the resettlement amount can be estimated. Revenues are recognized once the resettlement amount is received. There were no material MISO resettlements in 2018, 2017, or 2016.

Stock-based Compensation

Stock-based compensation cost is measured at the grant date based on the fair value of the award, net of an assumed forfeiture rate. Ameren recognizes as compensation expense the estimated fair value of stock-based compensation on a straight-line basis over the requisite vesting period. See Note 11 – Stock-based Compensation for additional information.

Deferred Compensation

As of December 31, 2018, and 2017, “Other deferred credits and liabilities” on Ameren’s balance sheet included deferred compensation obligations of $80 million and $86 million, respectively, recorded at the present value of future benefits to be paid.

Excise Taxes

Ameren Missouri and Ameren Illinois collect from their customers excise taxes, including municipal and state excise taxes and gross receipts taxes, that are levied on the sale or distribution of natural gas and electricity. The following table presents the excise taxes recorded on a gross basis in “Operating Revenues – Electric,” “Operating Revenues – Natural gas” and “Operating Expenses – Taxes other than income taxes” on the statements of income for the years ended December 31, 2018, 2017, and 2016:



	2018		2017			2016
Ameren Missouri	$	164	$	153		$	151
Ameren Illinois	118		112		^(a)	108		^(a)
Ameren	$	282	$	265		$	259


(a)	Amounts have been adjusted from those previously reported to reflect additional excise taxes for the years ended December 31, 2017 and 2016.

Unamortized Debt Discounts, Premiums, and Issuance Costs

Long-term debt discounts, premiums, and issuance costs are amortized over the lives of the related issuances. Credit agreement fees are amortized over the term of the agreement.

Income Taxes

Ameren uses an asset and liability approach for its financial accounting and reporting of income taxes. Deferred tax assets and liabilities are recognized for transactions that are treated differently for financial reporting and income tax return purposes. These deferred tax assets and liabilities are based on statutory tax rates.

We expect that regulators will reduce future revenues for deferred tax liabilities that were initially recorded at rates in excess of the current statutory rate. Therefore, reductions in certain deferred tax liabilities that were recorded because of decreases in the statutory rate have been credited to a regulatory liability. A regulatory asset has been established to recognize the probable recovery through future customer rates of tax benefits related to the equity component of allowance for funds used during construction, as well as the effects of tax rate increases. To the extent deferred tax balances are included in rate base, the revaluation of deferred taxes is recorded as a regulatory asset or liability on the balance sheet and will be collected from, or refunded to, customers. For deferred tax balances not included in rate base, the revaluation of deferred taxes is recorded as an adjustment to income tax expense on the income statement. See Note 12 – Income Taxes for further information regarding the revaluation of deferred taxes related to the TCJA and Missouri and Illinois state corporate income tax rate changes.

Ameren Missouri, Ameren Illinois, and all the other Ameren subsidiary companies are parties to a tax allocation agreement with Ameren (parent) that provides for the allocation of consolidated tax liabilities. The tax allocation agreement specifies that each party be allocated an amount of tax using a stand-alone calculation, which is similar to that which would be owed or refunded had the party been separately subject to tax considering the impact of consolidation. Any net benefit attributable to Ameren (parent) is reallocated to the other parties. This reallocation is treated as a capital contribution to the party receiving the benefit. See Note 13 – Related-party Transactions for information regarding capital contributions under the tax allocation agreement.

Earnings per Share

Earnings per basic and diluted share are computed by dividing “Net Income Attributable to Ameren Common Shareholders” by the weighted-average number of basic and diluted common shares outstanding, respectively, during the period. Earnings per diluted share reflects the potential dilution that would occur if certain stock-based performance share units and restricted stock units were settled. The number of shares from performance share units assumed to be settled was 2.0 million, 1.6 million, and 0.8 million for the years ended December 31, 2018, 2017, and 2016, respectively. The number of shares from restricted stock units assumed to be settled was immaterial for the year ended December 31, 2018, and not applicable for the years ended December 31, 2017 and 2016. There were no potentially dilutive securities excluded from the diluted earnings per share calculations for the years ended December 31, 2018, 2017, and 2016.

Accounting Changes and Other Matters

The following is a summary of recently adopted authoritative accounting guidance, as well as guidance issued but not yet adopted, that could affect the Ameren Companies.

In the first quarter of 2018, the Ameren Companies adopted authoritative accounting guidance on various topics. See the Operating Revenues section above for more information on our adoption of the guidance on revenue from contracts with customers. See Note 10 – Retirement Benefits for more information on our adoption of the guidance on the presentation of net periodic pension and postretirement benefit cost. See the Cash, Cash Equivalents, and Restricted Cash section above for more information on our adoption of the guidance on restricted cash. Our adoption of the guidance on the recognition and measurement of financial assets and financial liabilities did not have a material impact on our results of operations or financial position.

Leases

In February 2016, the FASB issued authoritative guidance that requires an entity to recognize assets and liabilities arising from all leases with a term greater than one year. This guidance will affect the Ameren Companies’ financial position by increasing the assets and liabilities recorded relating to operating leases. Ameren expects both its assets and liabilities to increase by approximately $40 million, largely due to an increase at Ameren Missouri. We do not expect the impacts of this guidance to be material to our results of operations or cash flows. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease will depend on its classification as a finance lease or operating lease. The guidance also requires additional disclosures to enable users of financial statements to understand the amount, timing, and uncertainty of cash flows arising from leases. We will adopt this guidance using the January 1, 2019 effective date as the date of our application of the standard. No adjustment to comparative periods will be made. This guidance will be effective for the Ameren Companies in the first quarter of 2019. See Note 14 – Commitments and Contingencies for additional information on our leases.

Measurement of Credit Losses on Financial Instruments

In June 2016, the FASB issued authoritative guidance that requires an entity to recognize an allowance for financial instruments that reflects its current estimate of credit losses expected to be incurred over the life of the financial instruments. The guidance requires an entity to measure expected credit losses using relevant information about past events, current conditions, and reasonable and supportable forecasts that affect the collectibility of the reported amount. We are currently assessing the impacts of this guidance on our results of operations, financial position, and disclosures. This guidance will be effective for the Ameren Companies in the first quarter of 2020, and will require changes to be applied retrospectively with a cumulative effect adjustment to retained earnings as of the adoption date.

Fair Value Measurement Disclosures

In August 2018, the FASB issued authoritative guidance that affects disclosure requirements for fair value measurements. This guidance will be effective for the Ameren Companies in the first quarter of 2020, with early adoption permitted. We are currently assessing the impacts of this guidance on our disclosures.

Defined Benefit Plan Disclosures

In August 2018, the FASB issued authoritative guidance that affects disclosure requirements for defined benefit plans. This guidance will be effective for the Ameren Companies in the fourth quarter of 2020, and will require changes to be applied retrospectively to each period presented. Early adoption is permitted. We are currently assessing the impacts of this guidance on our disclosures.

Implementation Costs Incurred in Certain Cloud Computing Arrangements

In August 2018, the FASB issued authoritative guidance that aligns the requirements for capitalizing implementation costs incurred in certain hosting arrangements with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. This guidance requires capitalized implementation costs to be expensed over the term of the hosting arrangement and presented in the same line item in the statement of income as the fees of the associated hosting arrangement. Capitalized implementation costs must be presented in the balance sheet in the same line item that a prepayment for the fees of the associated hosting arrangement would be presented, and payments for capitalized implementation costs must be classified in the statement of cash flows in the same manner as payments for hosting arrangement fees. The Ameren Companies early adopted this guidance in the third quarter of 2018 and applied the guidance prospectively to all implementation costs incurred after the date of adoption. Implementation costs capitalized in 2018 were immaterial.

Classification of Certain Cash Receipts and Cash Payments

In August 2016, the FASB issued authoritative guidance that specifies the classification and presentation of certain cash flow items to reduce diversity in practice. This guidance was effective for the Ameren Companies in the first quarter of 2018 and was applied retrospectively. Our adoption of this guidance did not result in material changes to previously reported cash flows from operating, investing, or financing activities.