Short-Term Debt And Liquidity (Narrative) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($) lender	Dec. 31, 2015
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	0.48
Credit Agreements 2012
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,500,000,000.0
Covenant terms, default provisions, maximum indebtedness	100,000,000
Multiyear Credit Facility
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 2,100,000,000
Number of lenders | lender	22
Line of credit facility, maximum borrowing capacity, per lender	$ 118,000,000
Actual debt-to-capital ratio	0.51
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	0.52%	0.11%