Acquisitions and Dispositions (Duke Energy Discontinued Operations) (Details) - USD ($) $ in Millions	3 Months Ended							12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations, net of tax	$ (2)	$ (2)	$ (2)	$ (598)	$ 180	$ (112)	$ 122	$ (6)	$ (408)	$ 177
International Energy [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations, net of tax									(534)	157
Midwest Generation Business [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations, net of tax									36	33
Other Disposal Groups [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations, net of tax									$ 90	$ (13)