Restructuring Expected Cost, Costs Recognized, and Costs to be Recognized - 2016 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense			$ 49,090	$ (7,263)	$ 49,482
2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	$ 67,794		67,794
Costs incurred and charged to expense	7,800	$ 40,000	47,794
Restructuring and Related Cost, Expected Cost Remaining	20,000		20,000
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense			39,943
Employee Severance [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	44,186		44,186
Costs incurred and charged to expense			39,686
Restructuring and Related Cost, Expected Cost Remaining	4,500		4,500
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense			7,188
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	7,219		7,219
Costs incurred and charged to expense			7,219
Restructuring and Related Cost, Expected Cost Remaining	0		0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense			1,959
Other Restructuring [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	16,389		16,389
Costs incurred and charged to expense			889
Restructuring and Related Cost, Expected Cost Remaining	15,500		15,500
Electricity Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	10,827		10,827
Costs incurred and charged to expense			8,827
Restructuring and Related Cost, Expected Cost Remaining	2,000		2,000
Gas Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	34,468		34,468
Costs incurred and charged to expense			23,968
Restructuring and Related Cost, Expected Cost Remaining	10,500		10,500
Water Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	20,061		20,061
Costs incurred and charged to expense			13,061
Restructuring and Related Cost, Expected Cost Remaining	7,000		7,000
Corporate, Non-Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	2,438		2,438
Costs incurred and charged to expense			1,938
Restructuring and Related Cost, Expected Cost Remaining	$ 500		$ 500