Investments in Debt and Equity Securities (Maturities) (Details) $ in Millions	Mar. 31, 2019 USD ($)
Debt Instrument [Line Items]
Due in one year or less	$ 74
Due after one through five years	537
Due after five through 10 years	577
Due after 10 years	1,259
Total	2,447
Duke Energy Carolinas [Member]
Debt Instrument [Line Items]
Due in one year or less	9
Due after one through five years	153
Due after five through 10 years	287
Due after 10 years	616
Total	1,065
Progress Energy [Member]
Debt Instrument [Line Items]
Due in one year or less	41
Due after one through five years	341
Due after five through 10 years	245
Due after 10 years	545
Total	1,172
Duke Energy Progress [Member]
Debt Instrument [Line Items]
Due in one year or less	21
Due after one through five years	251
Due after five through 10 years	196
Due after 10 years	415
Total	883
Duke Energy Florida [Member]
Debt Instrument [Line Items]
Due in one year or less	20
Due after one through five years	90
Due after five through 10 years	49
Due after 10 years	130
Total	289
Duke Energy Indiana [Member]
Debt Instrument [Line Items]
Due in one year or less	4
Due after one through five years	17
Due after five through 10 years	4
Due after 10 years	17
Total	$ 42