Other Income And Expenses (Other Income And Expenses) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014		Dec. 31, 2013
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction	[1]	$ 30	$ 34		$ 37
Interest income on industrial development revenue bonds	[1]	27	27		27
Interest and dividend income	[1],[2]	14	10		3
Other	[1]	3	8	[3]	2
Total miscellaneous income	[1]	74	79		69
Donations	[1]	15	10		12
Other	[1]	15	12		14
Total miscellaneous expense	[1]	30	22		26
Union Electric Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction		22	32		31
Interest income on industrial development revenue bonds		27	27		27
Interest and dividend income		1	1		0
Other		2	0		0
Total miscellaneous income		52	60		58
Donations		5	6		4
Other		6	6		7
Total miscellaneous expense		11	12		11
Ameren Illinois Company
Other Nonoperating Income (Expense) [Line Items]
Allowance for equity funds used during construction		8	2		6
Interest and dividend income	[2]	12	7		2
Other		1	8	[3]	2
Total miscellaneous income		21	17		10
Donations		5	4		4
Other		7	4		5
Total miscellaneous expense		$ 12	$ 8		$ 9

[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.