Investments in Debt and Equity Securities (All Debt and Equity Securities Through OCI and FV-NI - ASU 2016-01) (Details) $ in Millions	Jun. 30, 2018 USD ($)
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	$ 2,898
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	83
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	7,500
Ndtf [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	2,851
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	79
Cash and cash equivalents	116
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	7,124
Other Classification [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	47
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	4
Cash and cash equivalents	15
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	376
Duke Energy Carolinas [Member] | Ndtf [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1,549
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	47
Cash and cash equivalents	32
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	3,781
Progress Energy [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1,303
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	32
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	3,401
Progress Energy [Member] | Ndtf [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1,302
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	32
Cash and cash equivalents	84
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	3,343
Progress Energy [Member] | Other Classification [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1
Cash and cash equivalents	11
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	58
Duke Energy Progress [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1,002
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	25
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	2,628
Duke Energy Progress [Member] | Ndtf [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1,002
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	25
Cash and cash equivalents	46
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	2,627
Duke Energy Progress [Member] | Other Classification [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Cash and cash equivalents	1
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	1
Duke Energy Florida [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	301
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	7
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	764
Duke Energy Florida [Member] | Ndtf [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	300
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	7
Cash and cash equivalents	38
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	716
Duke Energy Florida [Member] | Other Classification [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	1
Cash and cash equivalents	1
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	48
Duke Energy Indiana [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Gain	36
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	1
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	$ 115