CONDENSED CONSOLIDATED STATEMENTS OF INCOME (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
OPERATING REVENUES	$ 692,714	$ 677,728
OPERATING EXPENSES
Fuel and purchased power	197,110	212,395
Operations and maintenance	265,682	226,071
Depreciation and amortization	144,825	127,627
Taxes other than income taxes	53,600	43,836
Other expenses	163	388
Total	661,380	610,317
OPERATING INCOME	31,334	67,411
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction	14,079	9,482
Pension and other postretirement non-service credits - net	12,859	6,095
Other income (Note 9)	3,985	480
Other expense (Note 9)	(3,229)	(3,680)
Total	27,694	12,377
INTEREST EXPENSE
Interest charges	58,954	51,864
Allowance for borrowed funds used during construction	(6,755)	(4,472)
Total	52,199	47,392
INCOME BEFORE INCOME TAXES	6,829	32,396
INCOME TAXES	(1,265)	4,211
NET INCOME	8,094	28,185
Less: Net income attributable to noncontrolling interests (Note 6)	4,873	4,873
NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 3,221	$ 23,312
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - BASIC (in shares)	112,017	111,728
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING - DILUTED (in shares)	112,493	112,195
EARNINGS PER WEIGHTED-AVERAGE COMMON SHARE OUTSTANDING
Net income attributable to common shareholders - basic (in dollars per share)	$ 0.03	$ 0.21
Net income attributable to common shareholders - diluted (in dollars per share)	$ 0.03	$ 0.21
APS
OPERATING REVENUES	$ 692,006	$ 677,589
OPERATING EXPENSES
Fuel and purchased power	202,010	217,104
Operations and maintenance	254,601	219,008
Depreciation and amortization	144,112	127,208
Taxes other than income taxes	53,242	43,564
Taxes other than income taxes	163	436
Total	654,128	607,320
OPERATING INCOME	37,878	70,269
OTHER INCOME (DEDUCTIONS)
Allowance for equity funds used during construction	14,079	9,482
Pension and other postretirement non-service credits - net	13,197	6,042
Other income (Note 9)	3,772	342
Other expense (Note 9)	(2,945)	(3,128)
Total	28,103	12,738
INTEREST EXPENSE
Interest charges	56,158	50,796
Allowance for borrowed funds used during construction	(6,755)	(4,472)
Total	49,403	46,324
INCOME BEFORE INCOME TAXES	16,578	36,683
INCOME TAXES	2,106	8,648
NET INCOME	14,472	28,035
Less: Net income attributable to noncontrolling interests (Note 6)	4,873	4,873
NET INCOME ATTRIBUTABLE TO COMMON SHAREHOLDERS	$ 9,599	$ 23,162