Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) $ in Millions	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
2019	$ 580
2020	442
2021	8
2022	505
2023	240
Thereafter	6,734
Total	8,509
Ameren (parent)
Debt Instrument [Line Items]
2020	350
Thereafter	350
Total	700
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	3
Union Electric Company
Debt Instrument [Line Items]
2019	580
2020	92
2021	8
2022	55
2023	240
Thereafter	3,054
Total	4,029
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	31
Ameren Illinois Company
Debt Instrument [Line Items]
2022	400
Thereafter	2,930
Total	3,330
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	34
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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