CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
NET INCOME	$ 280,945	$ 267,900	$ 481,447	$ 403,408
Derivative instruments:
Net unrealized gain (loss), net of tax expense	9	(29)	(754)	(595)
Reclassification of net realized loss, net of tax expense	710	798	2,480	2,564
Pension and other postretirement benefits activity, net of tax expense	790	804	(21)	633
Total other comprehensive income	1,509	1,573	1,705	2,602
COMPREHENSIVE INCOME	282,454	269,473	483,152	406,010
Less: Comprehensive income attributable to noncontrolling interests	4,873	4,873	14,620	14,620
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	277,581	264,600	468,532	391,390
APS
NET INCOME	289,129	274,093	491,143	418,281
Derivative instruments:
Net unrealized gain (loss), net of tax expense	9	(29)	(754)	(595)
Reclassification of net realized loss, net of tax expense	710	798	2,480	2,564
Pension and other postretirement benefits activity, net of tax expense	777	799	81	768
Total other comprehensive income	1,496	1,568	1,807	2,737
COMPREHENSIVE INCOME	290,625	275,661	492,950	421,018
Less: Comprehensive income attributable to noncontrolling interests	4,873	4,873	14,620	14,620
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 285,752	$ 270,788	$ 478,330	$ 406,398