Restructuring Expected Costs - 2016 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 666	$ (678)	$ 82,908	$ 7,417
2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	58,636		58,636
Restructuring and Related Cost, Cost Incurred to Date					$ 54,212
Restructuring			(156)
Remaining Costs to be Recognized at Period End	4,580		4,580
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring			79,011
Employee Severance [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	37,197		37,197
Restructuring and Related Cost, Cost Incurred to Date					39,855
Restructuring			(2,658)
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			568
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	5,375		5,375
Restructuring and Related Cost, Cost Incurred to Date					4,922
Restructuring			453
Remaining Costs to be Recognized at Period End	0		0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring			3,329
Other Restructuring [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	16,064		16,064
Restructuring and Related Cost, Cost Incurred to Date					9,435
Restructuring			2,049
Remaining Costs to be Recognized at Period End	4,580		4,580
Electricity Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	11,029		11,029
Restructuring and Related Cost, Cost Incurred to Date					9,025
Restructuring			696
Remaining Costs to be Recognized at Period End	1,308		1,308
Gas Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	30,287		30,287
Restructuring and Related Cost, Cost Incurred to Date					29,181
Restructuring			(791)
Remaining Costs to be Recognized at Period End	1,897		1,897
Water Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	14,678		14,678
Restructuring and Related Cost, Cost Incurred to Date					13,761
Restructuring			(302)
Remaining Costs to be Recognized at Period End	1,219		1,219
Corporate, Non-Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	2,642		2,642
Restructuring and Related Cost, Cost Incurred to Date					$ 2,245
Restructuring			241
Remaining Costs to be Recognized at Period End	$ 156		$ 156