Restructuring Expected Costs, Costs To-Date, Remaining Costs, and Costs During the Period - 2014 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended	$ 40,679	$ 587	$ 41,294	$ (8,828)
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended			34,919
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended			5,153
Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended			1,222
2014 Project [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	48,478		48,478
Restructuring and Related Cost, Cost Incurred to Date					$ 47,182
Costs recognized during the period ended			1,296
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	34,630		34,630
Restructuring and Related Cost, Cost Incurred to Date					34,373
Costs recognized during the period ended			257
Remaining Costs to be Recognized at Period End	0		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	8,849		8,849
Restructuring and Related Cost, Cost Incurred to Date					8,880
Costs recognized during the period ended			(31)
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	4,999		4,999
Restructuring and Related Cost, Cost Incurred to Date					3,929
Costs recognized during the period ended			1,070
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Electricity Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	20,610		20,610
Restructuring and Related Cost, Cost Incurred to Date					21,743
Costs recognized during the period ended			(1,133)
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Gas Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	13,631		13,631
Restructuring and Related Cost, Cost Incurred to Date					11,855
Costs recognized during the period ended			1,776
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Water Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	1,995		1,995
Restructuring and Related Cost, Cost Incurred to Date					1,940
Costs recognized during the period ended			55
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	12,242		12,242
Restructuring and Related Cost, Cost Incurred to Date					$ 11,644
Costs recognized during the period ended			598
Remaining Costs to be Recognized at Period End	$ 0		$ 0