Commitments And Contingencies (Schedule Of Estimated Purchased Power Commitments) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	$ 1,258	[1]
2018	828	[1]
2019	580	[1]
2020	229	[1]
2021	148	[1]
Thereafter	829	[1]
Total	3,872	[1]
Coal
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	599	[1]
2018	371	[1]
2019	311	[1]
2020	27	[1]
2021	0	[1]
Thereafter	0	[1]
Total	1,308	[1]
Natural Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	238	[1],[2]
2018	167	[1],[2]
2019	99	[1],[2]
2020	45	[1],[2]
2021	12	[1],[2]
Thereafter	43	[1],[2]
Total	604	[1],[2]
Nuclear Fuel
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	45	[1]
2018	70	[1]
2019	27	[1]
2020	38	[1]
2021	44	[1]
Thereafter	45	[1]
Total	269	[1]
Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	255	[1],[3]
2018	156	[1],[3]
2019	79	[1],[3]
2020	58	[1],[3]
2021	58	[1],[3]
Thereafter	478	[1],[3]
Total	1,084	[1],[3]
Methane Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	3	[1]
2018	4	[1]
2019	4	[1]
2020	5	[1]
2021	5	[1]
Thereafter	65	[1]
Total	86	[1]
Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	118	[1]
2018	60	[1]
2019	60	[1]
2020	56	[1]
2021	29	[1]
Thereafter	198	[1]
Total	521	[1]
Union Electric Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	751
2018	525
2019	408
2020	131
2021	104
Thereafter	370
Total	2,289
Union Electric Company | Coal
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	599
2018	371
2019	311
2020	27
2021	0
Thereafter	0
Total	1,308
Union Electric Company | Natural Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	43	[2]
2018	29	[2]
2019	15	[2]
2020	10	[2]
2021	5	[2]
Thereafter	18	[2]
Total	120	[2]
Union Electric Company | Nuclear Fuel
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	45
2018	70
2019	27
2020	38
2021	44
Thereafter	45
Total	269
Union Electric Company | Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	22
2018	22
2019	22
2020	22
2021	22
Thereafter	59
Total	169
Union Electric Company | Methane Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	3
2018	4
2019	4
2020	5
2021	5
Thereafter	65
Total	86
Union Electric Company | Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	39
2018	29
2019	29
2020	29
2021	28
Thereafter	183
Total	337
Ameren Illinois Company
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	464
2018	296
2019	167
2020	98
2021	44
Thereafter	444
Total	1,513
Ameren Illinois Company | Natural Gas
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	195	[2]
2018	138	[2]
2019	83	[2]
2020	35	[2]
2021	8	[2]
Thereafter	25	[2]
Total	484	[2]
Ameren Illinois Company | Purchased Power
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	233	[3]
2018	134	[3]
2019	57	[3]
2020	36	[3]
2021	36	[3]
Thereafter	419	[3]
Total	915	[3]
Ameren Illinois Company | Other
Unrecorded Unconditional Purchase Obligation, Fiscal Year Maturity [Abstract]
2017	36
2018	24
2019	27
2020	27
2021	0
Thereafter	0
Total	$ 114

[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.