Short-Term Debt And Liquidity (Narrative) (Details)	12 Months Ended
	Dec. 31, 2015 USD ($) lender	Dec. 31, 2014
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	$ 1,800,000,000.0
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 | lender	24
Line of credit facility, maximum borrowing capacity, per lender	$ 115,000,000
Actual debt-to-capital ratio	0.51
Minimum ratio of consolidated funds from operations plus interest expense to consolidated interest expense as of balance sheet date	2.0 to 1.0
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	0.11%	0.19%