Divestiture Transactions and Discontinued Operations Divestiture Transactions and DIscontinued Operations (Components of Assets and Liabilities on Consolidated Balance Sheet) (Details) - USD ($) $ in Millions		Jun. 30, 2016	Dec. 31, 2015
Assets of discontinued operations
Accumulated deferred income taxes, net		$ 14	$ 14
Total assets of discontinued operations		14	14
Liabilities of discontinued operations
Accounts payable and other current obligations		1	1
Asset retirement obligations	[1]	26	28
Total liabilities of discontinued operations		$ 27	$ 29

[1] (a)Ameren has demolished and completed its retirement obligations at the Hutsonville energy center. The remaining ARO liabilities relate to the abandoned Meredosia energy center.