Restructuring Expected Costs - 2016 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring	$ (5,623)	$ 5,043	$ 82,242	$ 8,095
2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	59,367		59,367
Restructuring and Related Cost, Cost Incurred to Date					$ 54,212
Restructuring			155
Remaining Costs to be Recognized at Period End	5,000		5,000
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring			79,660
Employee Severance [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	37,846		37,846
Restructuring and Related Cost, Cost Incurred to Date					39,855
Restructuring			(2,009)
Remaining Costs to be Recognized at Period End	0		0
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring			624
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	5,546		5,546
Restructuring and Related Cost, Cost Incurred to Date					4,922
Restructuring			624
Remaining Costs to be Recognized at Period End	0		0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring			1,958
Other Restructuring [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	15,975		15,975
Restructuring and Related Cost, Cost Incurred to Date					9,435
Restructuring			1,540
Remaining Costs to be Recognized at Period End	5,000		5,000
Electricity Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	11,234		11,234
Restructuring and Related Cost, Cost Incurred to Date					9,025
Restructuring			709
Remaining Costs to be Recognized at Period End	1,500		1,500
Gas Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	31,084		31,084
Restructuring and Related Cost, Cost Incurred to Date					29,181
Restructuring			(97)
Remaining Costs to be Recognized at Period End	2,000		2,000
Water Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	14,562		14,562
Restructuring and Related Cost, Cost Incurred to Date					13,761
Restructuring			(699)
Remaining Costs to be Recognized at Period End	1,500		1,500
Corporate, Non-Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	2,487		2,487
Restructuring and Related Cost, Cost Incurred to Date					$ 2,245
Restructuring			242
Remaining Costs to be Recognized at Period End	$ 0		$ 0