Long-Term Debt And Equity Financings (Schedule Of Maturities Of Long-Term Debt) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
2017	$ 681
2018	840
2019	581
2020	442
2021	8
Thereafter	4,774
Total	7,326
Parent Company
Debt Instrument [Line Items]
2020	350	[1]
Thereafter	350	[1]
Total	700	[1]
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	(6)
Union Electric Company
Debt Instrument [Line Items]
2017	431	[1]
2018	383	[1]
2019	581	[1]
2020	92	[1]
2021	8	[1]
Thereafter	2,524	[1]
Total	4,019	[1]
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	(25)
Ameren Illinois Company
Debt Instrument [Line Items]
2017	250	[1]
2018	457	[1]
Thereafter	1,900	[1]
Total	2,607	[1]
Debt Instrument, Unamortized Discount or Premium and Debt Issuance Costs	$ (19)

[1] Excludes unamortized discount and premium and debt issuance costs of $6 million, $25 million, and $19 million at Ameren (parent), Ameren Missouri, and Ameren Illinois, respectively.