Restructuring Expected Costs - 2016 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Restructuring	$ 5,043	$ (1,622)	$ 8,095	$ 615
2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	67,889		67,889
Restructuring and Related Cost, Cost Incurred to Date					$ 47,794
Restructuring			8,095
Remaining Costs to be Recognized at Period End	12,000		12,000
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring			5,507
Employee Severance [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	45,193		45,193
Restructuring and Related Cost, Cost Incurred to Date					39,686
Restructuring			5,507
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			80
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	7,299		7,299
Restructuring and Related Cost, Cost Incurred to Date					7,219
Restructuring			80
Remaining Costs to be Recognized at Period End	0		0
Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring			2,508
Other restructuring costs | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	15,397		15,397
Restructuring and Related Cost, Cost Incurred to Date					889
Restructuring			2,508
Remaining Costs to be Recognized at Period End	12,000		12,000
Electricity Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	11,157		11,157
Restructuring and Related Cost, Cost Incurred to Date					8,827
Restructuring			330
Remaining Costs to be Recognized at Period End	2,000		2,000
Gas Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	32,891		32,891
Restructuring and Related Cost, Cost Incurred to Date					23,968
Restructuring			5,423
Remaining Costs to be Recognized at Period End	3,500		3,500
Water Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	21,074		21,074
Restructuring and Related Cost, Cost Incurred to Date					13,061
Restructuring			2,013
Remaining Costs to be Recognized at Period End	6,000		6,000
Corporate, Non-Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	2,767		2,767
Restructuring and Related Cost, Cost Incurred to Date					$ 1,938
Restructuring			329
Remaining Costs to be Recognized at Period End	$ 500		$ 500