Short-Term Debt And Liquidity Short-Term Debt and Liquidity (Commercial Paper) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	$ 607		$ 13
Weighted Average Interest Rate	0.32%		0.54%
Peak Short Term Borrowings	907	[1]	78	[1]
Peak Short Term Borrowings Interest Rate	0.70%		0.85%
Ameren (parent)
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	328		13
Weighted Average Interest Rate	0.32%		0.54%
Peak Short Term Borrowings	503	[1]	78	[1]
Peak Short Term Borrowings Interest Rate	0.35%		0.85%
Union Electric Company
Line of Credit Facility [Line Items]
Average Daily Commercial Paper Borrowings Outstanding	146
Weighted Average Interest Rate	0.31%
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	242
Weighted Average Interest Rate	0.32%
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