Restructuring Expected Costs - 2016 Projects (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 87,865	$ 3,052
2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	59,584
Restructuring and Related Cost, Cost Incurred to Date			$ 54,212
Restructuring	(128)
Remaining Costs to be Recognized at Period End	5,500
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring	86,986
Employee Severance [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	38,848
Restructuring and Related Cost, Cost Incurred to Date			39,855
Restructuring	(1,007)
Remaining Costs to be Recognized at Period End	0
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring	47
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	4,969
Restructuring and Related Cost, Cost Incurred to Date			4,922
Restructuring	47
Remaining Costs to be Recognized at Period End	0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring	832
Other Restructuring [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	15,767
Restructuring and Related Cost, Cost Incurred to Date			9,435
Restructuring	832
Remaining Costs to be Recognized at Period End	5,500
Electricity Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	10,919
Restructuring and Related Cost, Cost Incurred to Date			9,025
Restructuring	394
Remaining Costs to be Recognized at Period End	1,500
Gas Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	31,799
Restructuring and Related Cost, Cost Incurred to Date			29,181
Restructuring	618
Remaining Costs to be Recognized at Period End	2,000
Water Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	14,763
Restructuring and Related Cost, Cost Incurred to Date			13,761
Restructuring	(998)
Remaining Costs to be Recognized at Period End	2,000
Corporate, Non-Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	2,103
Restructuring and Related Cost, Cost Incurred to Date			$ 2,245
Restructuring	(142)
Remaining Costs to be Recognized at Period End	$ 0