Acquisitions and Dispositions - Acquisitions (Narrative) (Details) - USD ($) shares in Millions, $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended
	Oct. 03, 2016	Oct. 31, 2016	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 31, 2016	Aug. 01, 2016
Business Acquisition [Line Items]
Business Combination, Integration Related Costs			$ 34	$ 23	$ 30	$ 16					$ 103
Asset Impairment Charges											282	$ 18	$ 106
Net Income (Loss) Attributable to Parent			703	954	686	716	$ (227)	$ 1,176	$ 509	$ 694	3,059	2,152	2,816
Long-term Debt			52,279				47,895				52,279	47,895
Asset retirement obligations assumed												22
Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 5,000
Long-term debt assumed	$ 2,002
Business Combination, Integration Related Costs											103	439	9
Asset Impairment Charges											7
Business Combination, After Tax Integration Related Costs												279	19
Revenues												367
Net Income (Loss) Attributable to Parent												20
Long-term Debt														$ 3,750
Facility Size															$ 4,900
Common stock issuances, including dividend reinvestment and employee benefits (in shares)		10.6
Forward Contract Indexed to Issuer's Equity, Indexed Shares										10.6
Proceeds from Issuance or Sale of Equity		$ 723
Duke Energy Progress [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs			4	4	4	2					14
Asset Impairment Charges											19	1	5
Net Income (Loss) Attributable to Parent			168	$ 246	$ 154	$ 147	60	271	$ 131	$ 137	715	599	$ 566
Long-term Debt			$ 7,357				$ 7,011				7,357	7,011
Interest Rate Contract [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Loss on Interest Rate Derivative Instruments Not Designated as Hedging Instruments												190
Sales [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs												10
Operating Expense [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs											64	101
Operating Income (Loss) [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs												46
Interest Expense [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs												234
August 2016 Term Loan Facility [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Long-term Line of Credit								750
Facility Size								$ 1,500
Other Expense [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs											$ 71	104
Other Expense [Member] | Operating Expense [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs												94
Other Expense [Member] | Operating Income (Loss) [Member] | Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Business Combination, Integration Related Costs												$ 10