Restructuring Restructuring Expected Costs, Costs To-Date, Remaining Costs, and Costs During the Period - 2014 Projects (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended	$ 2,237	$ (5,181)
Employee severance costs
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended	1,027
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended	1,114
Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended	96
2014 Project [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	51,439
Restructuring and Related Cost, Cost Incurred to Date			$ 47,182
Costs recognized during the period ended	2,237
Remaining Costs to be Recognized at Period End	2,020
2014 Project [Member] | Employee severance costs
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	35,400
Restructuring and Related Cost, Cost Incurred to Date			34,373
Costs recognized during the period ended	1,027
Remaining Costs to be Recognized at Period End	0
2014 Project [Member] | Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	9,994
Restructuring and Related Cost, Cost Incurred to Date			8,880
Costs recognized during the period ended	1,114
Remaining Costs to be Recognized at Period End	0
2014 Project [Member] | Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	6,045
Restructuring and Related Cost, Cost Incurred to Date			3,929
Costs recognized during the period ended	96
Remaining Costs to be Recognized at Period End	2,020
2014 Project [Member] | Electricity Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	24,098
Restructuring and Related Cost, Cost Incurred to Date			21,743
Costs recognized during the period ended	528
Remaining Costs to be Recognized at Period End	1,827
2014 Project [Member] | Gas Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	13,206
Restructuring and Related Cost, Cost Incurred to Date			11,855
Costs recognized during the period ended	1,264
Remaining Costs to be Recognized at Period End	87
2014 Project [Member] | Water Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	1,891
Restructuring and Related Cost, Cost Incurred to Date			1,940
Costs recognized during the period ended	(64)
Remaining Costs to be Recognized at Period End	15
2014 Project [Member] | Corporate Unallocated [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	12,244
Restructuring and Related Cost, Cost Incurred to Date			$ 11,644
Costs recognized during the period ended	509
Remaining Costs to be Recognized at Period End	$ 91