Supplemental Information on Oil and Gas Exploration and Production Activities (Unaudited) (Details 3)	12 Months Ended
	Dec. 31, 2011 Bcf	Dec. 31, 2010 Bcf	Dec. 31, 2009 Bcf
Net proved reserves
Purchases in place	20.8
Natural Gas Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			509.0
Net proved reserves, Ending balance	607.6	583.3	509.0
Natural Gas Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance	25.3	34.6
Revisions	(3.0)	(8.1)
Extensions, additions and discoveries	4.0	5.0
Production	(5.1)	(6.2)
Purchases in place	3.9
Net proved reserves, Ending balance	25.1	25.3
Proved Developed Reserves	21.9	22.6	23.4
Proved Undeveloped Reserve	3.3	2.7	11.2
Natural Gas Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance	558.0	474.4
Revisions	(359.0)	(119.9)
Extensions, additions and discoveries	103.1	108.5
Production	(19.0)	(13.8)
Purchases in place	304.2	109.8
Sales in place	(4.8)	(1.0)
Net proved reserves, Ending balance	582.5	558.0
Proved Developed Reserves	256.4	152.3	114.1
Proved Undeveloped Reserve	326.1	405.7	360.3
Natural Gas Liquids Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			7.1
Net proved reserves, Ending balance	17.7	33.0	7.1
Natural Gas Liquids Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance	23.2	1.3
Revisions	0.1	(0.6)
Extensions, additions and discoveries	1.6	2.0
Production	(0.3)	(0.3)
Purchases in place	0.0	20.8
Sales in place	(22.8)
Net proved reserves, Ending balance	1.8	23.2
Proved Developed Reserves	0.9	4.3	0.8
Proved Undeveloped Reserve	0.9	18.9	0.5
Natural Gas Liquids Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance	9.8	5.8
Revisions	(4.2)	2.0
Extensions, additions and discoveries	3.2	1.9
Production	(0.7)	(0.5)
Purchases in place	9.4	0.8
Sales in place	(2.0)	(0.2)
Net proved reserves, Ending balance	15.9	9.8
Proved Developed Reserves	6.3	3.5	2.3
Proved Undeveloped Reserve	9.6	6.3	3.5
U.S. [Member] | Natural Gas Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			496.5
Net proved reserves, Ending balance	599.4	572.6	496.5
U.S. [Member] | Natural Gas Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance	19.8	29.6
Revisions	(3.9)	(11.7)
Extensions, additions and discoveries	4.0	5.0
Production	(3.0)	(3.1)
Net proved reserves, Ending balance	16.9	19.8
Proved Developed Reserves	13.6	17.1	18.4
Proved Undeveloped Reserve	3.3	2.7	11.2
U.S. [Member] | Natural Gas Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance	552.8	466.9
Revisions	(359.0)	(119.1)
Extensions, additions and discoveries	103.1	108.5
Production	(18.6)	(12.3)
Purchases in place	304.2	109.8
Sales in place	0.0	(1.0)
Net proved reserves, Ending balance	582.5	552.8
Proved Developed Reserves	256.4	147.1	106.6
Proved Undeveloped Reserve	326.1	405.7	360.3
U.S. [Member] | Natural Gas Liquids Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			5.6
Net proved reserves, Ending balance	17.7	29.1	5.6
U.S. [Member] | Natural Gas Liquids Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance	21.2	0.4
Revisions	0.1	0.1
Extensions, additions and discoveries	1.6
Production	(0.2)	(0.1)
Purchases in place	0.0	20.8
Sales in place	(20.9)
Net proved reserves, Ending balance	1.8	21.2
Proved Developed Reserves	0.9	2.7	0.2
Proved Undeveloped Reserve	0.9	18.5	0.2
U.S. [Member] | Natural Gas Liquids Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance	7.9	5.2
Revisions	(4.2)	1.5
Extensions, additions and discoveries	3.2	0.6
Production	(0.4)	(0.2)
Purchases in place	9.4	0.8
Net proved reserves, Ending balance	15.9	7.9
Proved Developed Reserves	6.3	3.0	1.8
Proved Undeveloped Reserve	9.6	4.9	3.4
Canada [Member] | Natural Gas Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			12.5
Net proved reserves, Ending balance	8.2	10.7	12.5
Canada [Member] | Natural Gas Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance	5.5	5.0
Revisions	0.9	3.6
Production	(2.1)	(3.1)
Purchases in place	3.9
Net proved reserves, Ending balance	8.2	5.5
Proved Developed Reserves	8.2	5.5	5.0
Proved Undeveloped Reserve	0.0	0.0	0.0
Canada [Member] | Natural Gas Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance	5.2	7.5
Revisions	0.0	(0.8)
Production	0.4	(1.5)
Sales in place	(4.8)
Net proved reserves, Ending balance	0.0	5.2
Proved Developed Reserves	0.0	5.2	7.5
Proved Undeveloped Reserve	0.0	0.0	0.0
Canada [Member] | Natural Gas Liquids Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			0.0
Net proved reserves, Ending balance	0.0	0.0	0.0
Canada [Member] | Natural Gas Liquids Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance			0.0
Net proved reserves, Ending balance	0.0	0.0	0.0
Proved Developed Reserves	0.0	0.0	0.0
Proved Undeveloped Reserve	0.0	0.0	0.0
Canada [Member] | Natural Gas Liquids Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance			0.0
Net proved reserves, Ending balance	0.0	0.0	0.0
Proved Developed Reserves	0.0	0.0	0.0
Proved Undeveloped Reserve	0.0	0.0	0.0
Colombia [Member] | Natural Gas Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			0.0
Net proved reserves, Ending balance	0.0	0.0	0.0
Colombia [Member] | Natural Gas Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance			0.0
Net proved reserves, Ending balance	0.0	0.0	0.0
Proved Developed Reserves	0.0	0.0	0.0
Proved Undeveloped Reserve	0.0	0.0	0.0
Colombia [Member] | Natural Gas Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance			0.0
Net proved reserves, Ending balance		0.0	0.0
Proved Developed Reserves	0.0	0.0	0.0
Proved Undeveloped Reserve	0.0	0.0	0.0
Colombia [Member] | Natural Gas Liquids Reserves [Member]
Net proved reserves
Net proved reserves, Beginning balance			1.5
Net proved reserves, Ending balance	0.0	3.9	1.5
Colombia [Member] | Natural Gas Liquids Reserves [Member] | Consolidated Subsidiary [Member]
Net proved reserves
Net proved reserves, Beginning balance	2.0	0.9
Revisions	0.0	(0.7)
Extensions, additions and discoveries	0.0	2.0
Production	(0.1)	(0.2)
Sales in place	(1.9)
Net proved reserves, Ending balance	0.0	2.0
Proved Developed Reserves	0.0	1.6	0.6
Proved Undeveloped Reserve	0.0	0.4	0.3
Colombia [Member] | Natural Gas Liquids Reserves [Member] | Equity Companies [Member]
Net proved reserves
Net proved reserves, Beginning balance	1.9	0.6
Revisions	0.0	0.5
Extensions, additions and discoveries	0.0	1.3
Production	0.3	(0.3)
Sales in place	(1.6)	(0.2)
Net proved reserves, Ending balance	0.0	1.9
Proved Developed Reserves	0.0	0.5	0.5
Proved Undeveloped Reserve	0.0	1.4	0.1