Commitments And Contingencies (Schedule Of Lease Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies [Line Items]
Capital lease payments, due in one year	$ 32
Capital lease payments, due in two years	32
Capital lease payments, due in three years	33
Capital lease payments, due in four years	32
Capital lease payments, due in five years	264
Capital lease payments, After 5 Years	0
Capital lease payments, Total	393
Less Amount representing interest, due in one year	25
Less Amount representing interest, due in two years	25
Less Amount representing interest, due in three years	25
Less Amount representing interest, due in four years	24
Less Amount representing interest, due in 5 years	24
Less Amount representing interest, After 5 Years	0
Less Amount representing interest, Total	123
Present value of minimum capital lease payments, due in one year	7
Present value of minimum capital lease payments, due in two years	7
Present value of minimum capital lease payments, due in three years	8
Present value of minimum capital lease payments, due in four years	8
Present value of minimum capital lease payments, due in five years	240
Present value of minimum capital lease payments, After 5 Years	0
Present value of minimum capital lease payments, Total	270
Operating leases, due in one year	10
Operating leases, due in two years	8
Operating leases, due in three years	7
Operating leases, due in four years	6
Operating leases, due in five years	5
Operating leases, After 5 Years	9
Operating leases, Total	45
Total lease obligations, due in one year	17
Total lease obligations, due in two years	15
Total lease obligations, due in three years	15
Total lease obligations, due in four years	14
Total lease obligations, due in five years	245
Total lease obligations, After 5 Years	9
Total lease obligations, Total	315
Total rental expense	9	$ 11	$ 38
Union Electric Company
Commitments and Contingencies [Line Items]
Capital lease payments, due in one year	32
Capital lease payments, due in two years	32
Capital lease payments, due in three years	33
Capital lease payments, due in four years	32
Capital lease payments, due in five years	264
Capital lease payments, After 5 Years	0
Capital lease payments, Total	393
Less Amount representing interest, due in one year	25
Less Amount representing interest, due in two years	25
Less Amount representing interest, due in three years	25
Less Amount representing interest, due in four years	24
Less Amount representing interest, due in 5 years	24
Less Amount representing interest, After 5 Years	0
Less Amount representing interest, Total	123
Present value of minimum capital lease payments, due in one year	7
Present value of minimum capital lease payments, due in two years	7
Present value of minimum capital lease payments, due in three years	8
Present value of minimum capital lease payments, due in four years	8
Present value of minimum capital lease payments, due in five years	240
Present value of minimum capital lease payments, After 5 Years	0
Present value of minimum capital lease payments, Total	270
Operating leases, due in one year	8
Operating leases, due in two years	7
Operating leases, due in three years	6
Operating leases, due in four years	5
Operating leases, due in five years	5
Operating leases, After 5 Years	9
Operating leases, Total	40
Total lease obligations, due in one year	15
Total lease obligations, due in two years	14
Total lease obligations, due in three years	14
Total lease obligations, due in four years	13
Total lease obligations, due in five years	245
Total lease obligations, After 5 Years	9
Total lease obligations, Total	310
Total rental expense	8	10	34
Ameren Illinois Company
Commitments and Contingencies [Line Items]
Operating leases, due in one year	1
Operating leases, due in two years	0
Operating leases, due in three years	0
Operating leases, due in four years	0
Operating leases, due in five years	0
Operating leases, After 5 Years	0
Operating leases, Total	1
Total rental expense	$ 1	$ 1	$ 30