Investments in Debt Securities and Equity Securities (Available-for-sale, OCI - ASU 2016-01) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	$ 2,307	$ 2,307
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]
Debt securities, available-for-sale, realized gain	4	14
Debt securities, available-for-sale, realized loss	7	32
Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	2,131	2,131
Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	272	272
Corporate debt securities [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	5	5
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	10	10
Debt securities, available-for-sale	595	595
Corporate debt securities [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	1	1
Debt securities, available-for-sale	64	64
Municipal bonds [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	7	7
Debt securities, available-for-sale	346	346
Municipal bonds [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	1	1
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	1	1
Debt securities, available-for-sale	85	85
US treasury and government [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	5	5
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	25	25
Debt securities, available-for-sale	974	974
US treasury and government [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	1	1
Debt securities, available-for-sale	59	59
Other debt obligations [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	3	3
Debt securities, available-for-sale	141	141
Other debt obligations [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	1	1
Debt securities, available-for-sale	43	43
Duke Energy Carolinas [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	1,028	1,028
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]
Debt securities, available-for-sale, realized gain	4	13
Debt securities, available-for-sale, realized loss	6	24
Duke Energy Carolinas [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	1,046	1,046
Duke Energy Carolinas [Member] | Corporate debt securities [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	2	2
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	7	7
Debt securities, available-for-sale	372	372
Duke Energy Carolinas [Member] | Municipal bonds [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	2	2
Debt securities, available-for-sale	80	80
Duke Energy Carolinas [Member] | US treasury and government [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	1	1
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	14	14
Debt securities, available-for-sale	439	439
Duke Energy Carolinas [Member] | Other debt obligations [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	3	3
Debt securities, available-for-sale	137	137
Progress Energy [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	1,076	1,076
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]
Debt securities, available-for-sale, realized gain	0	1
Debt securities, available-for-sale, realized loss	1	8
Progress Energy [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	1,085	1,085
Progress Energy [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	66	66
Progress Energy [Member] | Corporate debt securities [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	3	3
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	3	3
Debt securities, available-for-sale	223	223
Progress Energy [Member] | Municipal bonds [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	5	5
Debt securities, available-for-sale	266	266
Progress Energy [Member] | Municipal bonds [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	1	1
Debt securities, available-for-sale	48	48
Progress Energy [Member] | US treasury and government [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	4	4
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	11	11
Debt securities, available-for-sale	535	535
Progress Energy [Member] | Other debt obligations [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	4	4
Duke Energy Progress [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	781	781
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]
Debt securities, available-for-sale, realized gain	0	1
Debt securities, available-for-sale, realized loss	1	6
Duke Energy Progress [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	823	823
Duke Energy Progress [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	8	8
Duke Energy Progress [Member] | Corporate debt securities [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	2	2
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	2	2
Debt securities, available-for-sale	162	162
Duke Energy Progress [Member] | Municipal bonds [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	5	5
Debt securities, available-for-sale	265	265
Duke Energy Progress [Member] | US treasury and government [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	3	3
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	8	8
Debt securities, available-for-sale	352	352
Duke Energy Progress [Member] | Other debt obligations [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	0	0
Debt securities, available-for-sale	2	2
Duke Energy Florida [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	295	295
Debt Securities, Available-for-sale, Realized Gain (Loss) [Abstract]
Debt securities, available-for-sale, realized loss	0	2
Duke Energy Florida [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	262	262
Duke Energy Florida [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	48	48
Duke Energy Florida [Member] | Corporate debt securities [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	1	1
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	1	1
Debt securities, available-for-sale	61	61
Duke Energy Florida [Member] | Municipal bonds [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	0	0
Debt securities, available-for-sale	1	1
Duke Energy Florida [Member] | Municipal bonds [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	1	1
Debt securities, available-for-sale	48	48
Duke Energy Florida [Member] | US treasury and government [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	1	1
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	3	3
Debt securities, available-for-sale	183	183
Duke Energy Florida [Member] | Other debt obligations [Member] | Ndtf [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized gain, before tax	0	0
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	0	0
Debt securities, available-for-sale	2	2
Duke Energy Indiana [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	40	40
Duke Energy Indiana [Member] | Other Classification [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	40	40
Duke Energy Indiana [Member] | Corporate debt securities [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale	8	8
Duke Energy Indiana [Member] | Municipal bonds [Member]
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain (Loss), before Tax [Abstract]
Debt securities, available-for-sale, accumulated gross unrealized loss, before tax	1	1
Debt securities, available-for-sale	$ 32	$ 32