Fair Value Measurements (Schedule Of Carrying Amounts And Estimated Fair Values Of Long-Term Debt And Preferred Stock) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt and Capital Lease Obligations	[1]	$ 7,276	$ 7,275
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]	7,772	7,814
Preferred stock	[1]	131	125
Union Electric Company | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt and Capital Lease Obligations		3,994	4,110
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)		4,304	4,449
Preferred stock		79	75
Ameren Illinois Company | Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt and Capital Lease Obligations		2,588	2,471
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)		2,765	2,665
Preferred stock		$ 52	$ 50

[1] Preferred stock is recorded in "Noncontrolling Interests" on the consolidated balance sheet.