Variable Interest Entities (Schedule of Non-Consolidated VIEs) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	$ 1,175	$ 925
Investments and other assets	2,960	2,769
Taxes Payable, Current	551	384
Other current liabilities	1,865	2,044
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	6,621	14,155
Other Liabilities	1,581	1,753
Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	919	751
Investments and other assets	17	12
Total assets	936	763
Taxes Payable, Current	(29)
Other current liabilities	4	3
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	42
Other Liabilities	12	13
Total liabilities	29	16
Net assets of non-consolidated VIEs	907	747
Pipeline Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	697	487
Investments and other assets	17	12
Total assets	714	499
Taxes Payable, Current	(29)
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	42
Total liabilities	13
Net assets of non-consolidated VIEs	701	499
Other VIEs [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	42	90
Total assets	42	90
Other current liabilities	4	3
Other Liabilities	12	13
Total liabilities	16	16
Net assets of non-consolidated VIEs	26	74
Commercial Renewables [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates	180	174
Total assets	180	174
Net assets of non-consolidated VIEs	180	174
Duke Energy Ohio [Member]
Variable Interest Entity [Line Items]
Receivables from affiliated companies	133	129
Investments and other assets	21	23
Taxes Payable, Current	190	178
Other current liabilities	71	91
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	781	1,443
Other Liabilities	108	166
Duke Energy Ohio [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Receivables from affiliated companies	87	82
Total assets	87	82
Net assets of non-consolidated VIEs	87	82
Duke Energy Indiana [Member]
Variable Interest Entity [Line Items]
Receivables from affiliated companies	125	114
Investments and other assets	189	147
Taxes Payable, Current	95	31
Other current liabilities	104	93
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	925	1,900
Other Liabilities	18	27
Duke Energy Indiana [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Receivables from affiliated companies	106	101
Total assets	106	101
Net assets of non-consolidated VIEs	106	101
Piedmont Natural Gas [Member]
Variable Interest Entity [Line Items]
Receivables from affiliated companies	7	7
Investments in equity method unconsolidated affiliates	61	212
Investments and other assets	65	21
Taxes Payable, Current	19	67
Other current liabilities	69	102
Deferred Income Taxes and Other Tax Liabilities, Noncurrent	564	931
Other Liabilities	$ 170	189
Piedmont Natural Gas [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]
Variable Interest Entity [Line Items]
Investments in equity method unconsolidated affiliates		139
Total assets		139
Other Liabilities		4
Total liabilities		4
Net assets of non-consolidated VIEs		$ 135