Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) $ in Millions	Dec. 31, 2015 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	$ 1,323	[1]
2017	1,145	[1]
2018	531	[1]
2019	342	[1]
2020	215	[1]
Thereafter	1,128	[1]
Total	4,684	[1]
Coal
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	664	[1]
2017	685	[1]
2018	204	[1]
2019	110	[1]
2020	0	[1]
Thereafter	0	[1]
Total	1,663	[1]
Natural Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	249	[1],[2]
2017	190	[1],[2]
2018	127	[1],[2]
2019	89	[1],[2]
2020	43	[1],[2]
Thereafter	60	[1],[2]
Total	758	[1],[2]
Nuclear Fuel
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	51	[1]
2017	46	[1]
2018	68	[1]
2019	24	[1]
2020	51	[1]
Thereafter	108	[1]
Total	348	[1]
Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	241	[1],[3]
2017	147	[1],[3]
2018	72	[1],[3]
2019	58	[1],[3]
2020	58	[1],[3]
Thereafter	539	[1],[3]
Total	1,115	[1],[3]
Methane Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	3	[1]
2017	4	[1]
2018	5	[1]
2019	5	[1]
2020	6	[1]
Thereafter	71	[1]
Total	94	[1]
Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	115	[1]
2017	73	[1]
2018	55	[1]
2019	56	[1]
2020	57	[1]
Thereafter	350	[1]
Total	706	[1]
Union Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	833
2017	826
2018	352
2019	205
2020	120
Thereafter	469
Total	2,805
Union Electric Company | Coal
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	664
2017	685
2018	204
2019	110
2020	0
Thereafter	0
Total	1,663
Union Electric Company | Natural Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	46	[2]
2017	36	[2]
2018	24	[2]
2019	14	[2]
2020	10	[2]
Thereafter	23	[2]
Total	153	[2]
Union Electric Company | Nuclear Fuel
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	51
2017	46
2018	68
2019	24
2020	51
Thereafter	108
Total	348
Union Electric Company | Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	23
2017	23
2018	23
2019	23
2020	23
Thereafter	84
Total	199
Union Electric Company | Methane Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	3
2017	4
2018	5
2019	5
2020	6
Thereafter	71
Total	94
Union Electric Company | Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	46
2017	32
2018	28
2019	29
2020	30
Thereafter	183
Total	348
Ameren Illinois Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	452
2017	303
2018	176
2019	137
2020	95
Thereafter	659
Total	1,822
Ameren Illinois Company | Natural Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	203	[2]
2017	154	[2]
2018	103	[2]
2019	75	[2]
2020	33	[2]
Thereafter	37	[2]
Total	605	[2]
Ameren Illinois Company | Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	218	[3]
2017	124	[3]
2018	49	[3]
2019	35	[3]
2020	35	[3]
Thereafter	455	[3]
Total	916	[3]
Ameren Illinois Company | Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2016	31
2017	25
2018	24
2019	27
2020	27
Thereafter	167
Total	$ 301

[1] (c)Includes amounts for Ameren registrant and nonregistrant subsidiaries.

[2] (a)Includes amounts for generation and for distribution.

[3] (b)The purchased power amounts for Ameren and Ameren Illinois include agreements through 2032 for renewable energy credits with various renewable energy suppliers. The agreements contain a provision that allows Ameren Illinois to reduce the quantity purchased in the event that Ameren Illinois would not be able to recover the costs associated with the renewable energy credits.