Investments in Debt and Equity Securities (All Debt and Equity Securities Through OCI and FV-NI - ASU 2016-01) (Details) $ in Millions	Sep. 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	$ 3,179
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	97
Debt securities, available-for-sale, and equity securities, FV-NI	7,790
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	3,127
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	93
Cash and cash equivalents	75
Debt securities, available-for-sale, and equity securities, FV-NI	7,403
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	52
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	4
Cash and cash equivalents	21
Debt securities, available-for-sale, and equity securities, FV-NI	387
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	1,695
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	55
Cash and cash equivalents	18
Debt securities, available-for-sale, and equity securities, FV-NI	3,936
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	1,433
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	38
Debt securities, available-for-sale, and equity securities, FV-NI	3,533
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	1,432
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	38
Cash and cash equivalents	57
Debt securities, available-for-sale, and equity securities, FV-NI	3,467
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	18
Debt securities, available-for-sale, and equity securities, FV-NI	66
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	1,106
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	29
Debt securities, available-for-sale, and equity securities, FV-NI	2,744
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	1,106
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	29
Cash and cash equivalents	42
Debt securities, available-for-sale, and equity securities, FV-NI	2,736
Duke Energy Progress [Member] | Other Classification [Member]
Schedule Of Available For Sale Securities And Other Trading Assets [Line Items]
Cash and cash equivalents	8
Debt securities, available-for-sale, and equity securities, FV-NI	8
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	327
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	9
Debt securities, available-for-sale, and equity securities, FV-NI	779
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	326
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	9
Cash and cash equivalents	15
Debt securities, available-for-sale, and equity securities, FV-NI	731
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	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	40
Debt securities, available-for-sale, and equity securities, FV-NI, unrealized loss	1
Debt securities, available-for-sale, and equity securities, FV-NI	$ 118