Acquisitions and Sales of Other Assets (Purchase Price Calculation) (Details) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Jul. 02, 2012	Mar. 31, 2012	Dec. 31, 2011
Significant Acquisitions and Disposals [Line Items]
Progress Energy common shares outstanding	706,000,000	704,000,000		446,000,000	445,000,000
Exchange ratio			87.083%
Fair value of outstanding earned stock compensation awards			$ 62
Total estimated purchase price			$ 18,071
Progress Energy [Member]
Significant Acquisitions and Disposals [Line Items]
Progress Energy common shares outstanding	100	100