CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
OPERATING REVENUES (NOTE 2)	$ 661,930	$ 740,530
OPERATING EXPENSES
Fuel and purchased power	188,521	230,588
Operations and maintenance	221,318	245,634
Depreciation and amortization	154,079	148,707
Taxes other than income taxes	56,768	55,090
Other expenses	822	427
Total	621,508	680,446
OPERATING INCOME	40,422	60,084
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction	7,697	11,188
Pension and other postretirement non-service credits - net	13,911	5,114
Other income (Note 9)	12,569	7,169
Other expense (Note 9)	(4,784)	(4,358)
Total	29,393	19,113
INTEREST EXPENSE
Interest charges	59,234	60,653
Allowance for borrowed funds used during construction	(4,076)	(6,665)
Total	55,158	53,988
INCOME BEFORE INCOME TAXES	14,657	25,209
INCOME TAXES	(20,209)	2,418
NET INCOME	34,866	22,791
Less: Net income attributable to noncontrolling interests (Note 6)	4,873	4,873
NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 29,993	$ 17,918
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - BASIC (in shares)	112,594	112,337
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - DILUTED (in shares)	112,862	112,735
EARNINGS PER WEIGHTED-AVERAGE COMMON SHARE OUTSTANDING
Net income attributable to common shareholders - basic (in dollars per share)	$ 0.27	$ 0.16
Net income attributable to common shareholders - diluted (in dollars per share)	$ 0.27	$ 0.16
APS
OPERATING REVENUES (NOTE 2)	$ 661,930	$ 740,530
OPERATING EXPENSES
Fuel and purchased power	188,521	230,588
Operations and maintenance	218,265	240,375
Depreciation and amortization	154,058	148,685
Taxes other than income taxes	56,758	55,078
Other expenses	822	427
Total	618,424	675,153
OPERATING INCOME	43,506	65,377
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction	7,697	11,188
Pension and other postretirement non-service credits - net	14,262	5,499
Other income (Note 9)	11,633	6,416
Other expense (Note 9)	(4,668)	(3,878)
Total	28,924	19,225
INTEREST EXPENSE
Interest charges	55,736	56,665
Allowance for borrowed funds used during construction	(4,076)	(6,665)
Total	51,660	50,000
INCOME BEFORE INCOME TAXES	20,770	34,602
INCOME TAXES	(19,448)	1,453
NET INCOME	40,218	33,149
Less: Net income attributable to noncontrolling interests (Note 6)	4,873	4,873
NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 35,345	$ 28,276