Divestiture Transactions and Discontinued Operations (Components of Discontinued Operations in Consolidated Statement of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating revenues	$ 0	$ 1	$ 1,037
Operating benefits (expenses)	1	(2)	(1,207)	[1]
Operating income (loss)	1	(1)	(170)
Other income (loss)	0	0	(1)
Interest charges	0	0	(39)
Income (loss) before income taxes	1	(1)	(210)
Income tax (expense) benefit	50	0	(13)
Income (Loss) from Discontinued Operations, Net of Tax (Note 16)	$ 51	$ (1)	(223)
Merchant Generation
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment of assets to be disposed of			$ 201

[1] (a)Includes a $201 million pretax loss on disposal relating to the New AER divestiture.