Income Taxes (Schedule Of Changes To Unrecognized Tax Benefits And Related Interest) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits	$ 54		$ 90		$ 156
Increases based on tax positions	2		6		7
Decreases based on tax positions	56		42		143
Increases based on tax positions related to current period	0				69
Decreases related to the lapse of statute of limitations					1
Unrecognized tax benefits	0		54		90
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	0		52		54
Union Electric Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits	0		31		136
Increases based on tax positions	0		1		0
Decreases based on tax positions	0		32		122
Increases based on tax positions related to current period	0		0		16
Changes related to settlements with taxing authorities			0
Decreases related to the lapse of statute of limitations					1
Unrecognized tax benefits	0		0		31
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	0		0		3
Ameren Illinois Company
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits	(1)		(1)		13
Increases based on tax positions	1		1		2
Decreases based on tax positions	0		1		16
Increases based on tax positions related to current period	0				0
Changes related to settlements with taxing authorities			0
Unrecognized tax benefits	0		(1)		(1)
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	0		(1)
Other
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits	55		60		7
Increases based on tax positions	1		4		5
Decreases based on tax positions	(56)	[1]	9		5
Increases based on tax positions related to current period	0				53	[1]
Changes related to settlements with taxing authorities			0
Unrecognized tax benefits	0		55		60
Total unrecognized tax benefits (detriments) that, if recognized, would impact the effective tax rates	$ 0		$ 53	[1]	$ 51	[1]

[1] Primarily due to tax positions relating to the New AER divestiture. The income statement impact of this unrecognized tax benefit was included in "Income (loss) from discontinued operations, net of taxes" on Ameren's consolidated statement of income (loss). See Note 16 – Divestiture Transactions and Discontinued Operations for additional information.