Short-Term Debt And Liquidity Short-Term Debt and Liquidity (Commercial Paper) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	$ 609		$ 26
Weighted Average Interest Rate	0.35%		0.52%
Peak Short Term Borrowings	907	[1]	92	[1]
Peak Short Term Borrowings Interest Rate	0.75%		0.85%
Ameren (parent)
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	386		26
Weighted Average Interest Rate	0.36%		0.52%
Peak Short Term Borrowings	531	[1]	92	[1]
Peak Short Term Borrowings Interest Rate	0.75%		0.85%
Union Electric Company
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	141
Weighted Average Interest Rate	0.38%
Peak Short Term Borrowings	495	[1]		[1]
Peak Short Term Borrowings Interest Rate	0.70%
Ameren Illinois Company
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	157
Weighted Average Interest Rate	0.31%
Peak Short Term Borrowings	$ 300	[1]		[1]
Peak Short Term Borrowings Interest Rate	0.34%

[1] (a)The timing of peak commercial paper issuances varies by company, and therefore the peak amounts presented by company might not equal the Ameren Consolidated peak