Divestiture Transactions and Discontinued Operations (Components of Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset retirement obligations	$ 373		$ 369
Assets of discontinued operations
Cash and cash equivalents					25
Accounts receivable and unbilled revenue			5
Materials and supplies			5
Property and plant, net			142
Accumulated deferred income taxes, net(a)	15	[1]	13	[1]
Total assets of discontinued operations	15		165
Liabilities of discontinued operations
Accounts payable and other current obligations	2		5
Asset retirement obligations(b)	31	[2]	40	[2]
Total liabilities of discontinued operations	33		45
Shutdown Of Meredosia And Hutsonville Energy Centers [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset retirement obligations	$ 31		$ 31

[1] (a)Balances primarily consist of deferred income tax assets related to the abandoned Meredosia and Hutsonville energy centers.

[2] (b)Includes AROs associated with the abandoned Meredosia and Hutsonville energy centers of $31 million at March 31, 2014, and December 31, 2013.