Restructuring Restructuring Expected Costs, Costs To-Date, Remaining Costs, and Costs During the Period - 2014 Projects (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended	$ (5)	$ 58	$ (9,686)	$ (2,211)
Employee severance costs
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended			(13,465)
Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended			1,395
Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Costs recognized during the period ended			2,384
2014 Project [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	50,396		50,396
Restructuring and Related Cost, Cost Incurred to Date					$ 55,800
Costs recognized during the period ended			(9,686)
Remaining Costs to be Recognized at Period End	4,282		4,282
2014 Project [Member] | Employee severance costs
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	33,982		33,982
Restructuring and Related Cost, Cost Incurred to Date					47,447
Costs recognized during the period ended			(13,465)
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Asset Impairment and Net (Gain) Loss on Sale or Disposal [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	9,347		9,347
Restructuring and Related Cost, Cost Incurred to Date					7,952
Costs recognized during the period ended			1,395
Remaining Costs to be Recognized at Period End	0		0
2014 Project [Member] | Other restructuring costs
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	7,067		7,067
Restructuring and Related Cost, Cost Incurred to Date					401
Costs recognized during the period ended			2,384
Remaining Costs to be Recognized at Period End	4,282		4,282
2014 Project [Member] | Electricity Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	25,924		25,924
Restructuring and Related Cost, Cost Incurred to Date					29,660
Costs recognized during the period ended			(7,790)
Remaining Costs to be Recognized at Period End	4,054		4,054
2014 Project [Member] | Gas Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	10,981		10,981
Restructuring and Related Cost, Cost Incurred to Date					12,185
Costs recognized during the period ended			(1,303)
Remaining Costs to be Recognized at Period End	99		99
2014 Project [Member] | Water Operating Segment [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	1,725		1,725
Restructuring and Related Cost, Cost Incurred to Date					1,106
Costs recognized during the period ended			597
Remaining Costs to be Recognized at Period End	22		22
2014 Project [Member] | Corporate Unallocated [Member]
Restructuring Cost and Reserve [Line Items]
Total expected costs at period end	11,766		11,766
Restructuring and Related Cost, Cost Incurred to Date					$ 12,849
Costs recognized during the period ended			(1,190)
Remaining Costs to be Recognized at Period End	$ 107		$ 107