Restructuring Expected Costs, Cost Recognized, and Remaining Costs to be Recognized - 2014 Projects (Details) - USD ($) $ in Thousands	12 Months Ended			15 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 49,090	$ (7,263)	$ 49,482
Employee severance costs
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	39,943
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	7,188
Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	1,959
2014 Project [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	48,478
Restructuring Charges	1,296			$ 47,182
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Electricity Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	20,610
Restructuring Charges	(1,133)			21,743
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Gas Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	13,631
Restructuring Charges	1,776			11,855
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Water Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	1,995
Restructuring Charges	55			1,940
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Corporate, Non-Segment [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	12,242
Restructuring Charges	598			11,644
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Employee severance costs
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	34,630
Restructuring Charges	257			34,373
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	8,849
Restructuring Charges	(31)			8,880
Restructuring and Related Cost, Expected Cost Remaining	0
2014 Project [Member] | Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Restructuring and Related Cost, Expected Cost	4,999
Restructuring Charges	1,070			$ 3,929
Restructuring and Related Cost, Expected Cost Remaining	$ 0