Financial Instruments Commodity Contract Volume (Details)	Dec. 31, 2015 MMcf
Regulated Distribution Segment [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	11,792
Regulated Distribution Segment [Member] | Nondesignated [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	11,792
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	91,440
Nonregulated Segment [Member] | Nondesignated [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	51,663
Nonregulated Segment [Member] | Fair Value Hedging [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	(23,528)
Nonregulated Segment [Member] | Cash Flow Hedging [Member]
Commodity Contract Outstanding Volumes [Line Items]
Investment Contract Volume	63,305