Acquisitions and Dispositions (Duke Energy Discontinued Operations) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (Loss) From Discontinued Operations, net of tax	$ (598)	$ 180	$ (112)	$ 122	$ 49	$ 45	$ (29)	$ 112	$ (408)	$ 177	$ (649)
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	(524)
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)	(52)
Discontinued Operations, Disposed of by Sale [Member] | 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	$ (73)