Investments in Debt and Equity Securities (All Debt and Equity Securities Through OCI and FV-NI - ASU 2016-01) (Details) $ in Millions	Mar. 31, 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	$ 2,823
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	74
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	7,414
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	2,765
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	71
Cash and cash equivalents	143
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	7,026
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	58
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	3
Cash and cash equivalents	15
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	388
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	1,507
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	39
Cash and cash equivalents	50
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	3,737
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	1,259
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	32
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	3,346
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	1,258
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	32
Cash and cash equivalents	93
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	3,289
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	10
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	57
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	966
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	25
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	2,572
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	966
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	25
Cash and cash equivalents	59
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	2,571
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	293
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	7
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	765
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	292
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	7
Cash and cash equivalents	34
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	718
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
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	47
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	48
Debt Securities, Available-for-sale, and Equity Securities, FV-NI, Unrealized Loss	1
Debt Securities, Available-for-sale, and Equity Securities, FV-NI	$ 127