Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
2018	$ 841
2019	581
2020	442
2021	8
2022	506
Thereafter	5,617
Total	7,995
Parent Company
Debt Instrument [Line Items]
2020	350
Thereafter	350
Total	700
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	4
Union Electric Company
Debt Instrument [Line Items]
2018	384
2019	581
2020	92
2021	8
2022	56
Thereafter	2,867
Total	3,988
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	27
Ameren Illinois Company
Debt Instrument [Line Items]
2018	457
2022	400
Thereafter	2,000
Total	2,857
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	27
Ameren Transmission Company of Illinois
Debt Instrument [Line Items]
2022	50
Thereafter	400
Total	450
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	$ 2

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