CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
NET INCOME	$ 319,885	$ 280,945	$ 499,591	$ 481,447
Derivative instruments:
Net unrealized gain (loss), net of tax expense	0	9	(96)	(754)
Reclassification of net realized loss, net of tax expense	451	710	1,316	2,480
Pension and other postretirement benefits activity, net of tax benefit	1,099	790	(2,740)	(21)
Total other comprehensive income	1,550	1,509	(1,520)	1,705
COMPREHENSIVE INCOME	321,435	282,454	498,071	483,152
Less: Comprehensive income attributable to noncontrolling interests	4,873	4,873	14,620	14,620
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	316,562	277,581	483,451	468,532
APS
NET INCOME	343,239	289,129	540,409	491,143
Derivative instruments:
Net unrealized gain (loss), net of tax expense	0	9	(96)	(754)
Reclassification of net realized loss, net of tax expense	451	710	1,316	2,480
Pension and other postretirement benefits activity, net of tax benefit	952	777	(2,955)	81
Total other comprehensive income	1,403	1,496	(1,735)	1,807
COMPREHENSIVE INCOME	344,642	290,625	538,674	492,950
Less: Comprehensive income attributable to noncontrolling interests	4,873	4,873	14,620	14,620
COMPREHENSIVE INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 339,769	$ 285,752	$ 524,054	$ 478,330