Other Income And Expenses (Other Income And Expenses) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	[1]	$ 27	$ 30	$ 34
Interest income on industrial development revenue bonds	[1]	27	27	27
Interest and dividend income	[1],[2]	13	14	10
Other	[1]	7	3	8	[3]
Total miscellaneous income	[1]	74	74	79
Donations	[1]	16	15	10
Other	[1]	16	15	12
Total miscellaneous expense	[1]	32	30	22
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction		23	22	32
Interest income on industrial development revenue bonds		27	27	27
Interest and dividend income		1	1	1
Other		1	2	0
Total miscellaneous income		52	52	60
Donations		4	5	6
Other		6	6	6
Total miscellaneous expense		10	11	12
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction		4	8	2
Interest and dividend income	[2]	12	12	7
Other		5	1	8	[3]
Total miscellaneous income		21	21	17
Donations		6	5	4
Other		6	7	4
Total miscellaneous expense		$ 12	$ 12	$ 8

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

[2] Includes Ameren Illinois' interest income on the IEIMA revenue requirement reconciliation adjustment regulatory assets.

[3] Includes Ameren Illinois' income earned in 2014 from customer-requested construction.