Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings Per Share [Abstract]
Income from continuing operations attributable to Duke Energy common stockholders, as adjusted for participating securities - basic	$ 1,702	$ 1,315	$ 1,061
Income from continuing operations attributable to Duke Energy common stockholders, as adjusted for participating securities - diluted	1,702	1,315	1,061
Average shares, basic	1,332	1,318	1,293
Stock options, performance and restricted stock	1	1	1
Average shares, diluted	1,333	1,319	1,294
EPS, basic	$ 1.28	$ 1.00	$ 0.82
EPS, diluted	$ 1.28	$ 1.00	$ 0.82
Value of stock options, performance and unvested stock awards not included in the effect of dilutive securities	7	13	20
Proceeds from sale of common stock		$ 288	$ 494