CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
NET INCOME	$ 267,900	$ 261,978	$ 403,408	$ 410,212
Derivative instruments:
Net unrealized gain (loss), net of tax benefit (expense)	(29)	(151)	(595)	(926)
Reclassification of net realized loss, net of tax benefit	798	892	2,564	3,742
Pension and other postretirement benefits activity, net of tax benefit (expense)	804	869	633	1,335
Total other comprehensive income	1,573	1,610	2,602	4,151
COMPREHENSIVE INCOME	269,473	263,588	406,010	414,363
Less: Comprehensive income attributable to noncontrolling interests	4,873	4,862	14,620	14,072
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	264,600	258,726	391,390	400,291
APS
NET INCOME	274,093	266,049	418,281	420,489
Derivative instruments:
Net unrealized gain (loss), net of tax benefit (expense)	(29)	(151)	(595)	(926)
Reclassification of net realized loss, net of tax benefit	798	892	2,564	3,742
Pension and other postretirement benefits activity, net of tax benefit (expense)	799	870	768	1,477
Total other comprehensive income	1,568	1,611	2,737	4,293
COMPREHENSIVE INCOME	275,661	267,660	421,018	424,782
Less: Comprehensive income attributable to noncontrolling interests	4,873	4,862	14,620	14,072
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 270,788	$ 262,798	$ 406,398	$ 410,710