Acquisitions and Dispositions (Midwest Generation Exit) (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 tax expense (benefit)								$ (6)	$ (30)	$ 89
Income (Loss) From Discontinued Operations, net of tax	$ (2)	$ (2)	$ (2)	$ (598)	$ 180	$ (112)	$ 122	(6)	(408)	177
Duke Energy Ohio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income tax expense (benefit)									(36)	22
Income (Loss) From Discontinued Operations, net of tax		$ (1)			$ 34		$ 2	$ (1)	36	23
Midwest Generation Business [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating Revenues										543
Loss on disposition										(45)
Income (loss) before income taxes										59
Income tax expense (benefit)									(36)	26
Income (Loss) From Discontinued Operations, net of tax									36	33
Midwest Generation Business [Member] | Duke Energy Ohio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Operating Revenues										412
Loss on disposition										(52)
Income (loss) before income taxes										44
Income tax expense (benefit)									(36)	21
Income (Loss) From Discontinued Operations, net of tax									$ 36	23
Antitrust Lawsuit [Member] | Duke Energy Ohio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Litigation Settlement, Expense										81
Antitrust Lawsuit [Member] | Midwest Generation Business [Member] | Duke Energy Ohio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Litigation Settlement, Expense										$ 81