Restructuring Expected Cost, Costs Recognized, and Costs to be Recognized - 2016 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		4 Months Ended	12 Months Ended			24 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Sep. 30, 2016
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense				$ 6,418	$ 49,090	$ (7,263)
2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				60,212
Costs incurred and charged to expense	$ 7,800	$ 40,000	$ 47,794	6,418
Restructuring and Related Cost, Expected Cost Remaining				6,000
2014 Project [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense							$ 48,500
Restructuring and Related Cost, Expected Cost Remaining				0
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense				169
Employee Severance [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				39,855
Costs incurred and charged to expense			39,686	169
Restructuring and Related Cost, Expected Cost Remaining				0
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense				(2,297)
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				4,922
Costs incurred and charged to expense			7,219	(2,297)
Restructuring and Related Cost, Expected Cost Remaining				0
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Costs incurred and charged to expense				8,546
Other Restructuring [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				15,435
Costs incurred and charged to expense			889	8,546
Restructuring and Related Cost, Expected Cost Remaining				6,000
Electricity Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				10,525
Costs incurred and charged to expense			8,827	198
Restructuring and Related Cost, Expected Cost Remaining				1,500
Gas Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				31,181
Costs incurred and charged to expense			23,968	5,213
Restructuring and Related Cost, Expected Cost Remaining				2,000
Water Operating Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				15,761
Costs incurred and charged to expense			13,061	700
Restructuring and Related Cost, Expected Cost Remaining				2,000
Corporate, Non-Segment [Member] | 2016 Projects [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost				2,745
Costs incurred and charged to expense			$ 1,938	307
Restructuring and Related Cost, Expected Cost Remaining				$ 500