Short-Term Debt And Liquidity (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Illinois Credit Agreement 2012 | Maximum
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,300,000,000.0
Illinois Credit Agreement 2012 | Ameren Illinois Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	800,000,000
Actual debt-to-capital ratio	0.47
Missouri Credit Agreement 2012 | Maximum
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,200,000,000.0
Missouri Credit Agreement 2012 | Union Electric Company
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	800,000,000
Actual debt-to-capital ratio	0.49
Credit Agreements 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	1,400,000,000.0
Covenant terms, default provisions, maximum indebtedness	75,000,000
Multiyear Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	2,100,000,000
Number of lenders	24
Line of credit facility, maximum borrowing capacity, per lender	115,000,000
Actual debt-to-capital ratio	0.50
Minimum ratio of consolidated funds from operations plus interest expense to consolidated interest expense as of balance sheet date	2.0 to 1.0
Letters of credit portion of aggregate commitment	25.00%
Line of Credit Facility, Commitment Fee Amount	100,000,000
Multiyear Credit Facility | Maximum
Line of Credit Facility [Line Items]
Actual debt-to-capital ratio	0.65
Utilities
Line of Credit Facility [Line Items]
Short Term Debt, Weighted Average Interest Rate During Period	0.19%	0.14%
New Ameren Energy Resources Company, LLC
Line of Credit Facility [Line Items]
Line of Credit Facility, Commitment Fee Amount	9,000,000