Commitments And Contingencies (Schedule Of Lease Obligations) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies [Line Items]
Capital lease payments, due in one year	[1],[2]	$ 33
Capital lease payments, due in two years	[1],[2]	32
Capital lease payments, due in three years	[1],[2]	32
Capital lease payments, due in four years	[1],[2]	32
Capital lease payments, due in five years	[1],[2]	32
Capital lease payments, After 5 Years	[1],[2]	297
Capital lease payments, Total	[1],[2]	458
Less Amount representing interest, due in one year	[2]	27
Less Amount representing interest, due in two years	[2]	26
Less Amount representing interest, due in three years	[2]	25
Less Amount representing interest, due in four years	[2]	25
Less Amount representing interest, due in 5 years	[2]	25
Less Amount representing interest, After 5 Years	[2]	48
Less Amount representing interest, Total	[2]	176
Present value of minimum capital lease payments, due in one year	[2]	6
Present value of minimum capital lease payments, due in two years	[2]	6
Present value of minimum capital lease payments, due in three years	[2]	7
Present value of minimum capital lease payments, due in four years	[2]	7
Present value of minimum capital lease payments, due in five years	[2]	7
Present value of minimum capital lease payments, After 5 Years	[2]	249
Present value of minimum capital lease payments, Total	[2]	282
Operating leases, due in one year	[2],[3]	13
Operating leases, due in two years	[2],[3]	12
Operating leases, due in three years	[2],[3]	12
Operating leases, due in four years	[2],[3]	11
Operating leases, due in five years	[2],[3]	10
Operating leases, After 5 Years	[2],[3]	23
Operating leases, Total	[2],[3]	81
Total lease obligations, due in one year	[2]	19
Total lease obligations, due in two years	[2]	18
Total lease obligations, due in three years	[2]	19
Total lease obligations, due in four years	[2]	18
Total lease obligations, due in five years	[2]	17
Total lease obligations, After 5 Years	[2]	272
Total lease obligations, Total	[2]	363
Annual obligation for real estate leases and railroad licenses		3
Total rental expense	[4]	38	$ 36	$ 37
Union Electric Company
Commitments and Contingencies [Line Items]
Capital lease payments, due in one year	[1]	33
Capital lease payments, due in two years	[1]	32
Capital lease payments, due in three years	[1]	32
Capital lease payments, due in four years	[1]	32
Capital lease payments, due in five years	[1]	32
Capital lease payments, After 5 Years	[1]	297
Capital lease payments, Total	[1]	458
Less Amount representing interest, due in one year		27
Less Amount representing interest, due in two years		26
Less Amount representing interest, due in three years		25
Less Amount representing interest, due in four years		25
Less Amount representing interest, due in 5 years		25
Less Amount representing interest, After 5 Years		48
Less Amount representing interest, Total		176
Present value of minimum capital lease payments, due in one year		6
Present value of minimum capital lease payments, due in two years		6
Present value of minimum capital lease payments, due in three years		7
Present value of minimum capital lease payments, due in four years		7
Present value of minimum capital lease payments, due in five years		7
Present value of minimum capital lease payments, After 5 Years		249
Present value of minimum capital lease payments, Total		282
Operating leases, due in one year	[3]	11
Operating leases, due in two years	[3]	11
Operating leases, due in three years	[3]	11
Operating leases, due in four years	[3]	10
Operating leases, due in five years	[3]	9
Operating leases, After 5 Years	[3]	21
Operating leases, Total	[3]	73
Total lease obligations, due in one year		17
Total lease obligations, due in two years		17
Total lease obligations, due in three years		18
Total lease obligations, due in four years		17
Total lease obligations, due in five years		16
Total lease obligations, After 5 Years		270
Total lease obligations, Total		355
Annual obligation for real estate leases and railroad licenses		2
Total rental expense		34	34	32
Ameren Illinois Company
Commitments and Contingencies [Line Items]
Operating leases, due in one year	[3]	1
Operating leases, due in two years	[3]	1
Operating leases, due in three years	[3]	1
Operating leases, due in four years	[3]	1
Operating leases, due in five years	[3]	1
Operating leases, After 5 Years	[3]	1
Operating leases, Total	[3]	6
Annual obligation for real estate leases and railroad licenses		1
Total rental expense		$ 30	$ 28	$ 25

[1] See Properties under Part I, Item 2, and Note 3 – Property, Plant, and Equipment, Net, of this report for additional information.

[2] ncludes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.

[3] Amounts related to certain land-related leases have indefinite payment periods. The annual obligations of $3 million, $2 million, and $1 million for Ameren, Ameren Missouri, and Ameren Illinois for these items are included in the 2017 through 2021 columns, respectively.

[4] Includes amounts for Ameren registrant and nonregistrant subsidiaries and intercompany eliminations.