Unconsolidated Investments 5 Narrative (Details) (USD $)	1 Months Ended	12 Months Ended					12 Months Ended			0 Months Ended	1 Months Ended		12 Months Ended	1 Months Ended
	Jan. 27, 2011	Dec. 31, 2011 Bcf MMcfperday megawatt	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Florida Gas Phase VIII Project [Member]	Apr. 30, 2011 Florida Gas Phase VIII Project [Member]	Dec. 31, 2011 Citrus [Member]	Dec. 31, 2010 Citrus [Member]	Dec. 31, 2011 Citrus [Member] Florida Gas Senior Notes Due July 2012 [Member]	May 02, 2011 Florida Gas [Member]	Aug. 19, 2010 Florida Gas [Member]	Jul. 19, 2010 Florida Gas [Member]	Dec. 31, 2011 Florida Gas [Member]	Jul. 30, 2010 Florida Gas [Member] Senior Notes Due 2020 [Member]	Jul. 30, 2010 Florida Gas [Member] Senior Notes Due 2015 [Member]
Schedule Of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		50.00%
Long-term debt due within one year		$ 343,254,000	$ 1,083,000				$ 686,500,000	$ 21,500,000
Equity Method Investment, Dividends or Distributions							0	0				98,600,000
Undistributed equity earnings		278,700,000	181,100,000
Net investment in excess of underlying equity		650,000,000	649,000,000
Estimated Cost						2,500,000,000
Years Firm Transportation Service Agreements					25
Contracted Capacity					74
Loan to unconsolidated investments					37,000,000
Expected Additional Loans To Equity Method Investment From Each Sponsor			100,000,000
Promissory Note with Unconsolidated Investment					150,000,000
Promissory Note Interest Rate					one-month Eurodollar rate plus a credit spread of 1.5 percent
Long term debt carrying value														500,000,000	350,000,000
Offering Price														99.826	99.982
Interest rate											7.625%			5.45%	4.00%
Principal per unit														100	100
Repayment of debt		18,556,000	140,947,000	60,623,000							325,000,000	83,000,000
Debt instrument, face amount									250,000,000
Regulatory asset unconsolidated investment		32,700,000
Regulatory liability unconsolidated investment		12,800,000
Proceeds From Legal Settlements	82,700,000			1,900,000
Amount Of Easement										15
Amount Of Temporary Work Space										75
Interest Awarded										8,000,000
Treatment facility capacity		200
Natural gas storage facility capacity		3.0
Natural gas-fired electric generation plant capacity		45
Percentage HCAs Assessments Required													96.00%
Estimate Required Modifications And Inspections Minimum													30,000,000
Estimate Required Modifications And Inspections Maximum													$ 40,000,000