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Consolidated Statement Of Cash Flows (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Cash Flows From Operating Activities:      
Net income (loss) $ 592us-gaap_ProfitLoss $ 295us-gaap_ProfitLoss $ (974)us-gaap_ProfitLoss
(Income) Loss from discontinued operations, net of tax 1us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax 223us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax 1,496us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax
Adjustments to reconcile net income to net cash provided by operating activities:      
Depreciation and amortization 710us-gaap_DepreciationAmortizationAndAccretionNet 666us-gaap_DepreciationAmortizationAndAccretionNet 633us-gaap_DepreciationAmortizationAndAccretionNet
Amortization of nuclear fuel 81us-gaap_AdjustmentForAmortization 71us-gaap_AdjustmentForAmortization 83us-gaap_AdjustmentForAmortization
Amortization of debt issuance costs and premium/discounts 22us-gaap_AmortizationOfFinancingCostsAndDiscounts 24us-gaap_AmortizationOfFinancingCostsAndDiscounts 20us-gaap_AmortizationOfFinancingCostsAndDiscounts
Deferred income taxes and investment tax credits, net 451us-gaap_DeferredIncomeTaxesAndTaxCredits 410us-gaap_DeferredIncomeTaxesAndTaxCredits 257us-gaap_DeferredIncomeTaxesAndTaxCredits
Allowance for equity funds used during construction (34)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity [1] (37)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity [1] (36)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity [1]
Share-based Compensation 25us-gaap_ShareBasedCompensation 27us-gaap_ShareBasedCompensation 29us-gaap_ShareBasedCompensation
Other (24)us-gaap_OtherNoncashIncomeExpense 23us-gaap_OtherNoncashIncomeExpense (7)us-gaap_OtherNoncashIncomeExpense
Changes in assets and liabilities:      
Receivables 31us-gaap_IncreaseDecreaseInReceivables (60)us-gaap_IncreaseDecreaseInReceivables 30us-gaap_IncreaseDecreaseInReceivables
Materials and supplies 3us-gaap_IncreaseDecreaseInInventories 60us-gaap_IncreaseDecreaseInInventories (28)us-gaap_IncreaseDecreaseInInventories
Accounts and wages payable 10us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities 81us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities (34)us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
Taxes accrued (44)us-gaap_IncreaseDecreaseInAccruedTaxesPayable (195)us-gaap_IncreaseDecreaseInAccruedTaxesPayable (4)us-gaap_IncreaseDecreaseInAccruedTaxesPayable
Regulatory assets and liabilities (281)us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities 29us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities 14us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
Assets, other 30us-gaap_IncreaseDecreaseInOtherOperatingAssets 20us-gaap_IncreaseDecreaseInOtherOperatingAssets 40us-gaap_IncreaseDecreaseInOtherOperatingAssets
Liabilities, other (28)us-gaap_IncreaseDecreaseInOtherOperatingLiabilities (14)us-gaap_IncreaseDecreaseInOtherOperatingLiabilities 5us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
Pension and other postretirement benefits (10)us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities (28)us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities (23)us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
Counterparty collateral, net 22us-gaap_IncreaseDecreaseInDepositOtherAssets 41us-gaap_IncreaseDecreaseInDepositOtherAssets 41us-gaap_IncreaseDecreaseInDepositOtherAssets
Premiums paid on long-term debt repurchases     (138)aee_PremiumRelatedToDebtRedemptions
Net cash provided by operating activities - continuing operations 1,557us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations 1,636us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations 1,404us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations
Net cash provided by operating activities - discontinued operations (6)us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations 57us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations 286us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations
Net cash provided by operating activities 1,551us-gaap_NetCashProvidedByUsedInOperatingActivities 1,693us-gaap_NetCashProvidedByUsedInOperatingActivities 1,690us-gaap_NetCashProvidedByUsedInOperatingActivities
Cash Flows From Investing Activities:      
Capital expenditures (1,785)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment (1,379)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment (1,063)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Nuclear fuel expenditures (74)us-gaap_PaymentsForNuclearFuel (45)us-gaap_PaymentsForNuclearFuel (91)us-gaap_PaymentsForNuclearFuel
Purchases of securities - nuclear decommissioning trust fund (405)us-gaap_PaymentsToAcquireOtherInvestments (214)us-gaap_PaymentsToAcquireOtherInvestments (403)us-gaap_PaymentsToAcquireOtherInvestments
Sales and maturities of securities - nuclear decommissioning trust fund 391us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments 196us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments 384us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments
Proceeds from Collection of Notes Receivable 95us-gaap_ProceedsFromCollectionOfNotesReceivable 6us-gaap_ProceedsFromCollectionOfNotesReceivable  
Contributions to Note Receivable (89)aee_ContributionstoNoteReceivable (5)aee_ContributionstoNoteReceivable  
Other 11us-gaap_PaymentsForProceedsFromOtherInvestingActivities 1us-gaap_PaymentsForProceedsFromOtherInvestingActivities 20us-gaap_PaymentsForProceedsFromOtherInvestingActivities
Net cash used in investing activities - continuing operations (1,856)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations (1,440)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations (1,153)us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations
Net cash used in investing activities - discontinued operations 139us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations (283)us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations (157)us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations
Net cash used in investing activities (1,717)us-gaap_NetCashProvidedByUsedInInvestingActivities (1,723)us-gaap_NetCashProvidedByUsedInInvestingActivities (1,310)us-gaap_NetCashProvidedByUsedInInvestingActivities
Cash Flows From Financing Activities:      
Dividends on common stock (390)us-gaap_PaymentsOfDividendsCommonStock (388)us-gaap_PaymentsOfDividendsCommonStock (382)us-gaap_PaymentsOfDividendsCommonStock
Dividends paid to noncontrolling interest holders (6)us-gaap_PaymentsOfDividendsMinorityInterest (6)us-gaap_PaymentsOfDividendsMinorityInterest (6)us-gaap_PaymentsOfDividendsMinorityInterest
Short-term debt and credit facility repayments, net 346us-gaap_ProceedsFromRepaymentsOfShortTermDebt 368us-gaap_ProceedsFromRepaymentsOfShortTermDebt (148)us-gaap_ProceedsFromRepaymentsOfShortTermDebt
Redemptions, repurchases, and maturities:      
Long-term debt (697)us-gaap_RepaymentsOfOtherLongTermDebt (399)us-gaap_RepaymentsOfOtherLongTermDebt (760)us-gaap_RepaymentsOfOtherLongTermDebt
Issuances:      
Long-term debt 898us-gaap_ProceedsFromIssuanceOfLongTermDebt 278us-gaap_ProceedsFromIssuanceOfLongTermDebt 882us-gaap_ProceedsFromIssuanceOfLongTermDebt
Capital issuance costs (11)us-gaap_PaymentOfFinancingAndStockIssuanceCosts (2)us-gaap_PaymentOfFinancingAndStockIssuanceCosts (16)us-gaap_PaymentOfFinancingAndStockIssuanceCosts
Other 1us-gaap_ProceedsFromPaymentsForOtherFinancingActivities   4us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
Net cash provided by (used in) financing activities 141us-gaap_NetCashProvidedByUsedInFinancingActivities (149)us-gaap_NetCashProvidedByUsedInFinancingActivities (426)us-gaap_NetCashProvidedByUsedInFinancingActivities
Net change in cash and cash equivalents (25)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease (179)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease (46)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
Cash and cash equivalents at beginning of year 30us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations 209us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations 255us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations
Cash and cash equivalents at end of year 5us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations 30us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations 209us-gaap_CashAndCashEquivalentsAtCarryingValueIncludingDiscontinuedOperations
Less: Cash and cash equivalents of discontinued operations at end of year     25us-gaap_DisposalGroupIncludingDiscontinuedOperationCashAndCashEquivalents
Cash and cash equivalents at beginning of year 30us-gaap_CashAndCashEquivalentsAtCarryingValue 184us-gaap_CashAndCashEquivalentsAtCarryingValue  
Cash and cash equivalents at end of year 5us-gaap_CashAndCashEquivalentsAtCarryingValue 30us-gaap_CashAndCashEquivalentsAtCarryingValue 184us-gaap_CashAndCashEquivalentsAtCarryingValue
Noncash financing activity – dividends on common stock     7us-gaap_DividendsPayableCurrentAndNoncurrent
Cash Paid (Refunded) During the Year:      
Interest net of capitalized 333us-gaap_InterestPaidNet 393us-gaap_InterestPaidNet 433us-gaap_InterestPaidNet
Income taxes, net (27)us-gaap_IncomeTaxesPaidNet 8us-gaap_IncomeTaxesPaidNet 1us-gaap_IncomeTaxesPaidNet
Union Electric Company      
Cash Flows From Operating Activities:      
Net income (loss) 393us-gaap_ProfitLoss
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
398us-gaap_ProfitLoss
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
419us-gaap_ProfitLoss
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Adjustments to reconcile net income to net cash provided by operating activities:      
Depreciation and amortization 442us-gaap_DepreciationAmortizationAndAccretionNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
419us-gaap_DepreciationAmortizationAndAccretionNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
407us-gaap_DepreciationAmortizationAndAccretionNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Amortization of nuclear fuel 81us-gaap_AdjustmentForAmortization
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
71us-gaap_AdjustmentForAmortization
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
83us-gaap_AdjustmentForAmortization
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
FAC prudence review charge   26aee_NoncashContestedFAC
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
 
Amortization of debt issuance costs and premium/discounts 7us-gaap_AmortizationOfFinancingCostsAndDiscounts
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
7us-gaap_AmortizationOfFinancingCostsAndDiscounts
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
6us-gaap_AmortizationOfFinancingCostsAndDiscounts
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Deferred income taxes and investment tax credits, net 245us-gaap_DeferredIncomeTaxesAndTaxCredits
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
65us-gaap_DeferredIncomeTaxesAndTaxCredits
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
287us-gaap_DeferredIncomeTaxesAndTaxCredits
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Allowance for equity funds used during construction (32)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(31)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(31)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Other 3us-gaap_OtherNoncashIncomeExpense
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
1us-gaap_OtherNoncashIncomeExpense
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
8us-gaap_OtherNoncashIncomeExpense
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Changes in assets and liabilities:      
Receivables (10)us-gaap_IncreaseDecreaseInReceivables
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(59)us-gaap_IncreaseDecreaseInReceivables
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
27us-gaap_IncreaseDecreaseInReceivables
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Materials and supplies 8us-gaap_IncreaseDecreaseInInventories
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
45us-gaap_IncreaseDecreaseInInventories
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(48)us-gaap_IncreaseDecreaseInInventories
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Accounts and wages payable 25us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
42us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(27)us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Taxes accrued (197)us-gaap_IncreaseDecreaseInAccruedTaxesPayable
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
100us-gaap_IncreaseDecreaseInAccruedTaxesPayable
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(46)us-gaap_IncreaseDecreaseInAccruedTaxesPayable
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Regulatory assets and liabilities (68)us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
68us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(50)us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Assets, other 52us-gaap_IncreaseDecreaseInOtherOperatingAssets
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
18us-gaap_IncreaseDecreaseInOtherOperatingAssets
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
15us-gaap_IncreaseDecreaseInOtherOperatingAssets
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Liabilities, other   (29)us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
14us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Pension and other postretirement benefits 1us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
2us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
2us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Premiums paid on long-term debt repurchases     (62)aee_PremiumRelatedToDebtRedemptions
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Net cash provided by operating activities 950us-gaap_NetCashProvidedByUsedInOperatingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
1,143us-gaap_NetCashProvidedByUsedInOperatingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
1,004us-gaap_NetCashProvidedByUsedInOperatingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Cash Flows From Investing Activities:      
Capital expenditures (747)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(648)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(595)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Nuclear fuel expenditures (74)us-gaap_PaymentsForNuclearFuel
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(45)us-gaap_PaymentsForNuclearFuel
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(91)us-gaap_PaymentsForNuclearFuel
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Purchases of securities - nuclear decommissioning trust fund (405)us-gaap_PaymentsToAcquireOtherInvestments
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(214)us-gaap_PaymentsToAcquireOtherInvestments
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(403)us-gaap_PaymentsToAcquireOtherInvestments
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Sales and maturities of securities - nuclear decommissioning trust fund 391us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
196us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
384us-gaap_ProceedsFromSaleAndMaturityOfOtherInvestments
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Money pool advances, net   (24)us-gaap_LoansAndLeasesReceivableRelatedPartiesPeriodIncreaseDecrease
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
24us-gaap_LoansAndLeasesReceivableRelatedPartiesPeriodIncreaseDecrease
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Tax grants received related to renewable energy properties     18aee_TaxGrantsReceivedRelatedToRenewableEnergyProperties
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Other (2)us-gaap_PaymentsForProceedsFromOtherInvestingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
  8us-gaap_PaymentsForProceedsFromOtherInvestingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Net cash used in investing activities (837)us-gaap_NetCashProvidedByUsedInInvestingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(687)us-gaap_NetCashProvidedByUsedInInvestingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(703)us-gaap_NetCashProvidedByUsedInInvestingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Cash Flows From Financing Activities:      
Dividends on common stock (340)us-gaap_PaymentsOfDividendsCommonStock
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(460)us-gaap_PaymentsOfDividendsCommonStock
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(400)us-gaap_PaymentsOfDividendsCommonStock
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Return of capital to parent (215)us-gaap_PaymentsOfCapitalDistribution
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
   
Dividends on preferred stock (3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Money pool borrowings, net (105)us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
105us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
 
Short-term debt and credit facility repayments, net 97us-gaap_ProceedsFromRepaymentsOfShortTermDebt
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
   
Redemptions, repurchases, and maturities:      
Long-term debt (109)us-gaap_RepaymentsOfOtherLongTermDebt
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(249)us-gaap_RepaymentsOfOtherLongTermDebt
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(427)us-gaap_RepaymentsOfOtherLongTermDebt
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Issuances:      
Long-term debt 350us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
  482us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Capital issuance costs (3)us-gaap_PaymentOfFinancingAndStockIssuanceCosts
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
  (7)us-gaap_PaymentOfFinancingAndStockIssuanceCosts
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Capital contribution from parent 215us-gaap_ProceedsFromContributionsFromParent
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
4us-gaap_ProceedsFromContributionsFromParent
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
1us-gaap_ProceedsFromContributionsFromParent
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Net cash provided by (used in) financing activities (113)us-gaap_NetCashProvidedByUsedInFinancingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(603)us-gaap_NetCashProvidedByUsedInFinancingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(354)us-gaap_NetCashProvidedByUsedInFinancingActivities
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Net change in cash and cash equivalents   (147)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(53)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Cash and cash equivalents at beginning of year 1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
148us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
201us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Cash and cash equivalents at end of year 1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
148us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Noncash Or Part Noncash Capital Contribution From Parent 9aee_NoncashOrPartNoncashCapitalContributionFromParent
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
   
Cash Paid (Refunded) During the Year:      
Interest net of capitalized 203us-gaap_InterestPaidNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
212us-gaap_InterestPaidNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
220us-gaap_InterestPaidNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Income taxes, net 215us-gaap_IncomeTaxesPaidNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
86us-gaap_IncomeTaxesPaidNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
(3)us-gaap_IncomeTaxesPaidNet
/ dei_LegalEntityAxis
= aee_UnionElectricCompanyMember
Ameren Illinois Company      
Cash Flows From Operating Activities:      
Net income (loss) 204us-gaap_ProfitLoss
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
163us-gaap_ProfitLoss
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
144us-gaap_ProfitLoss
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Adjustments to reconcile net income to net cash provided by operating activities:      
Depreciation and amortization 259us-gaap_DepreciationAmortizationAndAccretionNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
238us-gaap_DepreciationAmortizationAndAccretionNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
214us-gaap_DepreciationAmortizationAndAccretionNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Amortization of debt issuance costs and premium/discounts 13us-gaap_AmortizationOfFinancingCostsAndDiscounts
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
15us-gaap_AmortizationOfFinancingCostsAndDiscounts
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
11us-gaap_AmortizationOfFinancingCostsAndDiscounts
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Deferred income taxes and investment tax credits, net 196us-gaap_DeferredIncomeTaxesAndTaxCredits
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
104us-gaap_DeferredIncomeTaxesAndTaxCredits
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
104us-gaap_DeferredIncomeTaxesAndTaxCredits
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Allowance for equity funds used during construction (2)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(6)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(5)us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Other (19)us-gaap_OtherNoncashIncomeExpense
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
4us-gaap_OtherNoncashIncomeExpense
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(11)us-gaap_OtherNoncashIncomeExpense
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Changes in assets and liabilities:      
Receivables (13)us-gaap_IncreaseDecreaseInReceivables
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
50us-gaap_IncreaseDecreaseInReceivables
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
23us-gaap_IncreaseDecreaseInReceivables
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Materials and supplies (4)us-gaap_IncreaseDecreaseInInventories
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
15us-gaap_IncreaseDecreaseInInventories
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
20us-gaap_IncreaseDecreaseInInventories
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Accounts and wages payable 7us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
19us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(21)us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Taxes accrued (7)us-gaap_IncreaseDecreaseInAccruedTaxesPayable
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
28us-gaap_IncreaseDecreaseInAccruedTaxesPayable
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
3us-gaap_IncreaseDecreaseInAccruedTaxesPayable
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Regulatory assets and liabilities (215)us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(35)us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
64us-gaap_IncreaseDecreaseInRegulatoryAssetsAndLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Assets, other 15us-gaap_IncreaseDecreaseInOtherOperatingAssets
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
5us-gaap_IncreaseDecreaseInOtherOperatingAssets
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
19us-gaap_IncreaseDecreaseInOtherOperatingAssets
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Liabilities, other 1us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
10us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
11us-gaap_IncreaseDecreaseInOtherOperatingLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Pension and other postretirement benefits (6)us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(8)us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(26)us-gaap_IncreaseDecreaseInEmployeeRelatedLiabilities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Counterparty collateral, net 14us-gaap_IncreaseDecreaseInDepositOtherAssets
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
43us-gaap_IncreaseDecreaseInDepositOtherAssets
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
40us-gaap_IncreaseDecreaseInDepositOtherAssets
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Premiums paid on long-term debt repurchases     (76)aee_PremiumRelatedToDebtRedemptions
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Net cash provided by operating activities 445us-gaap_NetCashProvidedByUsedInOperatingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
651us-gaap_NetCashProvidedByUsedInOperatingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
519us-gaap_NetCashProvidedByUsedInOperatingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Cash Flows From Investing Activities:      
Capital expenditures (835)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(701)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(442)us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Other 7us-gaap_PaymentsForProceedsFromOtherInvestingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
6us-gaap_PaymentsForProceedsFromOtherInvestingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
5us-gaap_PaymentsForProceedsFromOtherInvestingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Net cash used in investing activities (828)us-gaap_NetCashProvidedByUsedInInvestingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(695)us-gaap_NetCashProvidedByUsedInInvestingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(437)us-gaap_NetCashProvidedByUsedInInvestingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Cash Flows From Financing Activities:      
Dividends on common stock   (110)us-gaap_PaymentsOfDividendsCommonStock
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(189)us-gaap_PaymentsOfDividendsCommonStock
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Dividends on preferred stock (3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(3)us-gaap_PaymentsOfDividendsPreferredStockAndPreferenceStock
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Money pool borrowings, net (41)us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
32us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
24us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInMoreThanThreeMonths
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Short-term debt and credit facility repayments, net 32us-gaap_ProceedsFromRepaymentsOfShortTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
   
Redemptions, repurchases, and maturities:      
Long-term debt (163)us-gaap_RepaymentsOfOtherLongTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(150)us-gaap_RepaymentsOfOtherLongTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(333)us-gaap_RepaymentsOfOtherLongTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Issuances:      
Long-term debt 548us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
278us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
400us-gaap_ProceedsFromIssuanceOfLongTermDebt
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Capital issuance costs (6)us-gaap_PaymentOfFinancingAndStockIssuanceCosts
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(2)us-gaap_PaymentOfFinancingAndStockIssuanceCosts
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(6)us-gaap_PaymentOfFinancingAndStockIssuanceCosts
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Capital contribution from parent 15us-gaap_ProceedsFromContributionsFromParent
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
   
Other 1us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
  4us-gaap_ProceedsFromPaymentsForOtherFinancingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Net cash provided by (used in) financing activities 383us-gaap_NetCashProvidedByUsedInFinancingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
45us-gaap_NetCashProvidedByUsedInFinancingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(103)us-gaap_NetCashProvidedByUsedInFinancingActivities
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Net change in cash and cash equivalents   1us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
(21)us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Cash and cash equivalents at beginning of year 1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
  21us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Cash and cash equivalents at end of year 1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
1us-gaap_CashAndCashEquivalentsAtCarryingValue
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
 
Cash Paid (Refunded) During the Year:      
Interest net of capitalized 110us-gaap_InterestPaidNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
112us-gaap_InterestPaidNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
125us-gaap_InterestPaidNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
Income taxes, net $ (44)us-gaap_IncomeTaxesPaidNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
$ (23)us-gaap_IncomeTaxesPaidNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
$ (22)us-gaap_IncomeTaxesPaidNet
/ dei_LegalEntityAxis
= aee_AmerenIllinoisCompanyMember
[1] Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.