Divestiture Transactions and Discontinued Operations Divestiture Transactions and Discontinued Operations (Components of Assets and Liabilities on Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Assets of discontinued operations
Accumulated deferred income taxes, net	$ 17	$ 15
Total assets of discontinued operations	17	15
Liabilities of discontinued operations
Accounts payable and other current obligations	1	1
Asset retirement obligations	29	32
Total liabilities of discontinued operations	$ 30	$ 33