Income Taxes (Schedule Of Effective Income Tax Rate Reconciliation) (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Statutory federal income tax rate:	35.00%	35.00%	35.00%
Depreciation differences	(1.00%)
Amortization of investment tax credit	(1.00%)	(1.00%)	(1.00%)
State tax	5.00%	4.00%	4.00%
Other permanent items		1.00%	0.00%
Effective income tax rate	38.00%	39.00%	38.00%
Union Electric Company
Income Taxes [Line Items]
Statutory federal income tax rate:	35.00%	35.00%	35.00%
Depreciation differences	0.00%		0.00%
Amortization of investment tax credit	(1.00%)	(1.00%)	(1.00%)
State tax	3.00%	3.00%	3.00%
Other permanent items	0.00%	0.00%	1.00%
Effective income tax rate	37.00%	37.00%	38.00%
Ameren Illinois Company
Income Taxes [Line Items]
Statutory federal income tax rate:	35.00%	35.00%	35.00%
Depreciation differences	(2.00%)		(1.00%)
Amortization of investment tax credit	0.00%	0.00%	0.00%
State tax	5.00%	6.00%	6.00%
Other permanent items	(1.00%)
Effective income tax rate	37.00%	41.00%	40.00%