Short-Term Debt And Liquidity Short-Term Debt and Liquidity (Commercial Paper) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	$ 539		$ 2
Weighted Average Interest Rate	0.45%		0.80%
Peak Short Term Borrowings	700	[1]	21	[1]
Peak Short Term Borrowings Interest Rate	0.75%		0.85%
Ameren (parent) [Domain]
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	339		2
Weighted Average Interest Rate	0.45%		0.80%
Peak Short Term Borrowings	452	[1]	21	[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	200
Weighted Average Interest Rate	0.45%
Peak Short Term Borrowings	$ 290	[1]		[1]
Peak Short Term Borrowings Interest Rate	0.70%

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