Investments in Debt and Equity Securities (Realized Gains and Losses)(Details) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	$ 93
Realized losses	62
Duke Energy Carolinas [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	66
Realized losses	40
Progress Energy [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	27
Realized losses	21
Duke Energy Progress [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	24
Realized losses	19
Duke Energy Florida [Member]
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Realized gains	3
Realized losses	$ 2