Acquisitions and Dispositions (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2016
Business Acquisition [Line Items]
Asset retirement obligations assumed	$ 226	$ 4
Subsequent Event [Member] | International Energy [Member]
Business Acquisition [Line Items]
Segment Carrying Value			$ 2,700
Piedmont Natural Gas [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	$ 4,900
Business Acquisition, Share Price	$ 60
Long-term debt assumed	$ 1,900
Forward starting interest rate swaps, notional	900
Bridge Facility	4,900
Acquiree Termination Fee	125
Acquirer Termination Fee	250
Duke Energy Progress [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	1,249
Asset retirement obligations assumed	204
Duke Energy Progress [Member] | NCEMPA Generating Assets [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross	1,250
Acquisition adjustment, recorded within property, plant and equipment	350
Nuclear decommissioning trust fund assets transferred	287
Asset retirement obligations assumed	204
Duke Energy Ohio [Member] | Midwest Generation Business [Member]
Business Acquisition [Line Items]
Proceeds from sale of business	$ 2,800