Divestiture Transactions and Discontinued Operations (Components of Assets and Liabilities on Consolidated Balance Sheet) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Assets of discontinued operations
Accumulated deferred income taxes, net		$ 14	$ 15
Total assets of discontinued operations		14	15	$ 165
Liabilities of discontinued operations
Accounts payable and other current obligations		1	1
Asset retirement obligations	[1]	28	32
Total liabilities of discontinued operations		$ 29	$ 33

[1] (a)Ameren is demolishing the Hutsonville energy center and expects to demolish the Meredosia energy center beginning in 2016.