Contingent Value Obligations (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Feb. 15, 2012	Dec. 31, 2010
Contingent Value Obligations [Line Items]
CVO's in connection with the acquisition of Florida Progress during 2000	98.6
CVO's repurchased in connection with the negotiated settlement agreement and subsequent tender offer	80.1	83.4
CVO's outstanding	18.5
CVO trust	$ 11		$ 11
CVO liability	802		552
CVO purchase price	0.75
CVO mark-to-market	59
Derivatives not designated as hedging instruments
Contingent Value Obligations [Line Items]
CVO liability	706		513
CVOs | Other liabilities, current | Derivatives not designated as hedging instruments
Contingent Value Obligations [Line Items]
CVO liability	14
CVOs | Other liabilities and deferred credits | Derivatives not designated as hedging instruments
Contingent Value Obligations [Line Items]
CVO liability			$ 15