Financial Instruments Commodity Contract Volume (Details)	Jun. 30, 2016 MMcf
Regulated Distribution Segment [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	10,002
Regulated Distribution Segment [Member] | Nondesignated [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	10,002
Regulated Distribution Segment [Member] | Fair Value Hedging [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	0
Regulated Distribution Segment [Member] | Cash Flow Hedging [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	0
Nonregulated Segment [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	61,335
Nonregulated Segment [Member] | Nondesignated [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	51,128
Nonregulated Segment [Member] | Fair Value Hedging [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	(35,118)
Nonregulated Segment [Member] | Cash Flow Hedging [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	45,325