Acquisitions and Dispositions Acquisitions and Dispositions (Assets Held For Sale) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Significant Acquisitions and Disposals [Line Items]
Charge for settlement agreement									$ 53
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Income tax expense (benefit)									19	$ (295)	$ 29
Income (Loss) From Discontinued Operations, net of tax	$ (9)	$ (5)	$ (57)	$ 91	$ 2	$ 378	$ (113)	$ (843)	20	(576)	86
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Current assets					364					364
Current liabilities					262					262
Midwest Generation Business [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Operating Revenues									543	1,748	1,885
Loss on disposition									(45)	(929)
Income (loss) before income taxes									59	(818)	141
Income tax expense (benefit)									26	(294)	56
Income (Loss) From Discontinued Operations, net of tax									33	(524)	85
Other Disposal Groups [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Income (Loss) From Discontinued Operations, net of tax									(13)	(52)	1
Duke Energy Ohio [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Income tax expense (benefit)									22	(300)	32
Income (Loss) From Discontinued Operations, net of tax		$ (2)	$ (65)	$ 90	34	$ 413	$ (135)	$ (875)	23	(563)	35
Disposal Group, Including Discontinued Operation, Balance Sheet Disclosures [Abstract]
Current assets					316					316
Current liabilities					$ 246					246
Duke Energy Ohio [Member] | Midwest Generation Business [Member]
Disposal Group, Including Discontinued Operation, Income Statement Disclosures [Abstract]
Operating Revenues									412	1,299	1,503
Loss on disposition									(52)	(959)
Income (loss) before income taxes									44	(863)	67
Income tax expense (benefit)									21	$ (300)	$ 32
Antitrust Lawsuit [Member]
Significant Acquisitions and Disposals [Line Items]
Charge for settlement agreement									81
Antitrust Lawsuit [Member] | Duke Energy Ohio [Member]
Significant Acquisitions and Disposals [Line Items]
Charge for settlement agreement									$ 81