CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Unaudited) - USD ($) $ in Thousands		Total	Common Stock	Treasury Stock	Retained Earnings		Accumulated Other Comprehensive Income (Loss)		Noncontrolling Interests	APS	APS Common Stock	APS Additional Paid-In Capital	APS Retained Earnings		APS Accumulated Other Comprehensive Income (Loss)		APS Noncontrolling Interests
Beginning balance (in shares) at Dec. 31, 2017			111,816,170	64,463							71,264,947
Balance at beginning of period at Dec. 31, 2017		$ 5,135,730	$ 2,614,805	$ (5,624)	$ 2,442,511		$ (45,002)		$ 129,040	$ 5,385,869	$ 178,162	$ 2,571,696	$ 2,533,954		$ (26,983)		$ 129,040
Increase (Decrease) in Shareholders' Equity
Net Income		499,591			484,971				14,620	540,409			525,789				14,620
Other comprehensive income (loss)		(1,520)					(1,520)			(1,735)					(1,735)
Dividends on common stock		(155,607)			(155,607)					(155,601)			(155,601)
Issuance of common stock (in shares)			199,779
Issuance of common stock		14,822	$ 14,822
Purchase of treasury stock (in shares)	[1]			(81,278)
Purchase of treasury stock	[1]	(6,285)		$ (6,285)
Reissuance of treasury stock for stock-based compensation and other (in shares)				128,373
Reissuance of treasury stock for stock-based compensation and other		10,501		$ 10,500	1
Capital activities by noncontrolling interests		11,372							11,372	11,372							11,372
Reclassification of income tax effects related to new tax reform		(8,552)			8,552	[2]	(8,552)	[2]					5,038	[3]	(5,038)	[3]
Other		1							1	1							1
Ending balance (in shares) at Sep. 30, 2018			112,015,949	17,368							71,264,947
Balance at end of period at Sep. 30, 2018		5,485,861	$ 2,629,627	$ (1,409)	2,780,428		(55,074)		132,289	5,757,571	$ 178,162	2,571,696	2,909,180		(33,756)		132,289
Beginning balance (in shares) at Jun. 30, 2018			111,990,222	17,633							71,264,947
Balance at beginning of period at Jun. 30, 2018		5,159,434	$ 2,624,672	$ (1,431)	2,465,402		(56,624)		127,415	5,412,930	$ 178,162	2,571,696	2,570,816		(35,159)		127,415
Increase (Decrease) in Shareholders' Equity
Net Income		319,885			315,012				4,873	343,239			338,366				4,873
Other comprehensive income (loss)		1,550					1,550			1,403					1,403
Dividends on common stock		14			14
Issuance of common stock (in shares)			25,727
Issuance of common stock		4,955	$ 4,955
Purchase of treasury stock (in shares)	[4]			(101)
Purchase of treasury stock	[4]	(8)		$ (8)
Reissuance of treasury stock for stock-based compensation and other (in shares)				366
Reissuance of treasury stock for stock-based compensation and other		30		$ 30	0
Other		1							1	(1)			(2)				1
Ending balance (in shares) at Sep. 30, 2018			112,015,949	17,368							71,264,947
Balance at end of period at Sep. 30, 2018		$ 5,485,861	$ 2,629,627	$ (1,409)	2,780,428		(55,074)		132,289	5,757,571	$ 178,162	2,571,696	2,909,180		(33,756)		132,289
Beginning balance (in shares) at Dec. 31, 2018		112,159,896	112,159,896	58,135							71,264,947
Balance at beginning of period at Dec. 31, 2018		$ 5,348,705	$ 2,634,265	$ (4,825)	2,641,183		(47,708)		125,790	5,786,797	$ 178,162	2,721,696	2,788,256		(27,107)		125,790
Increase (Decrease) in Shareholders' Equity
Net Income		488,959			474,339				14,620	511,942			497,322				14,620
Other comprehensive income (loss)		1,170					1,170			804					804
Dividends on common stock		(165,631)			(165,631)					(165,600)			(165,600)
Issuance of common stock (in shares)			243,855
Issuance of common stock		20,165	$ 20,165
Purchase of treasury stock (in shares)	[1]			(75,894)
Purchase of treasury stock	[1]	(6,892)		$ (6,892)
Reissuance of treasury stock for stock-based compensation and other (in shares)				76,082
Reissuance of treasury stock for stock-based compensation and other		6,600		$ 6,600	0
Capital activities by noncontrolling interests		11,372							11,372	11,372							11,372
Other		$ 1							1	0			(1)				1
Ending balance (in shares) at Sep. 30, 2019		112,403,751	112,403,751	57,947							71,264,947
Balance at end of period at Sep. 30, 2019		$ 5,681,705	$ 2,654,430	$ (5,117)	2,949,891		(46,538)		129,039	6,122,571	$ 178,162	2,721,696	3,119,977		(26,303)		129,039
Beginning balance (in shares) at Jun. 30, 2019			112,361,595	58,219							71,264,947
Balance at beginning of period at Jun. 30, 2019		5,357,243	$ 2,648,234	$ (5,140)	2,637,620		(47,636)		124,165	5,797,857	$ 178,162	2,721,696	2,801,110		(27,276)		124,165
Increase (Decrease) in Shareholders' Equity
Net Income		317,149			312,276				4,873	323,743			318,870				4,873
Other comprehensive income (loss)		1,098					1,098			973					973
Dividends on common stock		(5)			(5)
Issuance of common stock (in shares)			42,156
Issuance of common stock		6,196	$ 6,196
Purchase of treasury stock (in shares)	[4]			(103)
Purchase of treasury stock	[4]	(10)		$ (10)
Reissuance of treasury stock for stock-based compensation and other (in shares)				375
Reissuance of treasury stock for stock-based compensation and other		33		$ 33	0
Other		$ 1							1	(2)			(3)				1
Ending balance (in shares) at Sep. 30, 2019		112,403,751	112,403,751	57,947							71,264,947
Balance at end of period at Sep. 30, 2019		$ 5,681,705	$ 2,654,430	$ (5,117)	$ 2,949,891		$ (46,538)		$ 129,039	$ 6,122,571	$ 178,162	$ 2,721,696	$ 3,119,977		$ (26,303)		$ 129,039

[1] Primarily represents shares of common stock withheld from certain stock awards for tax purposes.

[2] In 2018, the Company adopted new accounting guidance and elected to reclassify income tax effects of the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) on items within accumulated other comprehensive income to retained earnings.

[3] In 2018, the Company adopted new accounting guidance and elected to reclassify income tax effects of the Tax Act on items within accumulated other comprehensive income to retained earnings.

[4] Primarily represents shares of common stock withheld from certain stock awards for tax purposes.