Guarantees (Details 5) (USD $)	Dec. 31, 2012
Guarantor Obligations [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 59,700,000
Fixed maximum amounts guaranteed, due next fiscal year	38,700,000
Fixed maximum amounts guaranteed, due in two years	2,200,000
Fixed maximum amounts guaranteed, due in three years	300,000
Fixed maximum amounts guaranteed, due in four years	100,000
Fixed maximum amounts guaranteed, due in six years	600,000
Fixed maximum amounts guaranteed, due in seven years	300,000
Expires on a specified number of days after the receipt of written notice	13,500,000
Fixed maximum amounts guaranteed by year no maturity date	4,000,000
Amount outstanding under guarantees that are reflected on balance sheet	600,000
Letters of credit	25,000,000
Outstanding letters of credit	0
Natural gas transportation and storage agreement fixed maximum amount of performance guarantee of a related party	5,000,000
The amount outstanding by a related party under the guarantee	900,000
Amount of surety bonds outstanding	$ 488,000,000