Financial Instruments Commodity Contract Volume (Details)	Jun. 30, 2013 MMcf
Natural Gas Distribution Segment [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	14,649
Natural Gas Distribution Segment [Member] | Nondesignated [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	14,649
Natural Gas Distribution Segment [Member] | Fair Value Hedging [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	0
Natural Gas Distribution Segment [Member] | Cash Flow Hedging [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	0
Nonregulated Segment [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	79,790
Nonregulated Segment [Member] | Nondesignated [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	75,520
Nonregulated Segment [Member] | Fair Value Hedging [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	(22,250)
Nonregulated Segment [Member] | Cash Flow Hedging [Member]
Debt Instrument [Line Items]
Investment Contract Volume 1	26,520