Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt and Capital Lease Obligations	[1]	$ 7,275	$ 6,205
Preferred stock	[1]	142	142
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt and capital lease obligations (including current portion)	[1]	7,814	7,135
Preferred stock	[1]	125	122
Union Electric Company | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt and Capital Lease Obligations		4,110	3,981
Preferred stock		80	80
Union Electric Company | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt and capital lease obligations (including current portion)		4,449	4,518
Preferred stock		75	73
Ameren Illinois Company | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt and Capital Lease Obligations		2,471	2,224
Preferred stock		62	62
Ameren Illinois Company | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt and capital lease obligations (including current portion)		2,665	2,517
Preferred stock		$ 50	$ 49

[1] Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.(b)Carrying amounts reflect the adoption of the new authoritative accounting guidance for the presentation of debt issuance costs. See Note 1 – Summary of Significant Accounting Policies