Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
OPERATING REVENUES	$ 893.4	$ 609.3	$ 1,493.6	$ 1,181.9
OPERATING EXPENSES:
Fuel and purchased power	229.7	111.8	365.2	225.6
SPP network transmission costs	68.4	61.8	136.0	122.4
Operating and maintenance	283.8	139.6	423.8	275.0
Depreciation and amortization	128.0	94.0	217.7	182.7
Taxes other than income tax	56.6	41.9	100.5	84.6
Total Operating Expenses	766.5	449.1	1,243.2	890.3
INCOME FROM OPERATIONS	126.9	160.2	250.4	291.6
OTHER INCOME (EXPENSE):
Investment earnings	(1.6)	(1.1)	(1.3)	(2.5)
Non-operating income	1.7	0.5	3.7	1.8
Non-operating expenses	(13.8)	(7.7)	(24.4)	(18.1)
Total Other Income (Expense)	(10.5)	(6.1)	(19.4)	(13.8)
Interest expense	58.4	43.7	102.2	84.8
INCOME BEFORE INCOME TAXES	58.0	110.4	128.8	193.0
Income tax expense (benefit)	(45.0)	35.9	(35.8)	56.8
Equity in earnings of equity method investees, net of income taxes	1.4	1.5	2.7	3.3
NET INCOME	104.4	76.0	167.3	139.5
Less: Net income attributable to noncontrolling interests	2.6	3.9	5.0	7.8
NET INCOME	$ 101.8	$ 72.1	$ 162.3	$ 131.7
Basic earnings per common share (in dollars per share)	$ 0.56	$ 0.50	$ 1.00	$ 0.92
Diluted earnings per common share (in dollars per share)	$ 0.56	$ 0.50	$ 1.00	$ 0.92
Average number of basic common shares outstanding (in shares)	180.9	142.5	161.9	142.5
Average number of diluted common shares outstanding (in shares)	181.0	142.6	162.0	142.6
DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.4	$ 0.4	$ 0.80	$ 0.80
Westar Energy Inc [Member]
OPERATING REVENUES	$ 650.9	$ 609.3	$ 1,251.1	$ 1,181.9
OPERATING EXPENSES:
Fuel and purchased power	158.0	111.8	293.5	225.6
SPP network transmission costs	68.4	61.8	136.0	122.4
Operating and maintenance	209.7	139.6	349.7	275.0
Depreciation and amortization	96.1	94.0	185.7	182.7
Taxes other than income tax	42.6	41.9	86.6	84.6
Total Operating Expenses	574.8	449.1	1,051.5	890.3
INCOME FROM OPERATIONS	76.1	160.2	199.6	291.6
OTHER INCOME (EXPENSE):
Investment earnings	0.0	(1.1)	(0.4)	(2.5)
Non-operating income	1.6	0.5	3.6	1.8
Non-operating expenses	(10.4)	(7.7)	(20.9)	(18.1)
Total Other Income (Expense)	(8.8)	(6.1)	(17.7)	(13.8)
Interest expense	44.4	43.7	88.2	84.8
INCOME BEFORE INCOME TAXES	22.9	110.4	93.7	193.0
Income tax expense (benefit)	(53.6)	35.9	(44.4)	56.8
Equity in earnings of equity method investees, net of income taxes	1.1	1.5	2.4	3.3
NET INCOME	77.6	76.0	140.5	139.5
Less: Net income attributable to noncontrolling interests	2.6	3.9	5.0	7.8
NET INCOME	75.0	72.1	$ 135.5	$ 131.7
DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)			$ 0.80	$ 0.80
KCPL [Member]
OPERATING REVENUES	452.2	482.7	$ 849.3	$ 878.6
OPERATING EXPENSES:
Fuel and purchased power	132.5	130.2	250.0	223.4
Operating and maintenance	104.5	113.8	227.2	236.4
Depreciation and amortization	70.2	68.3	137.1	133.6
Taxes other than income tax	30.3	44.2	59.3	88.8
Total Operating Expenses	337.5	356.5	673.6	682.2
INCOME FROM OPERATIONS	114.7	126.2	175.7	196.4
OTHER INCOME (EXPENSE):
Investment earnings	(0.8)	(0.5)	(1.4)	(1.0)
Non-operating income	(1.5)	1.2	1.5	3.2
Non-operating expenses	(6.0)	(14.7)	(13.9)	(28.8)
Total Other Income (Expense)	(6.7)	(13.0)	(11.0)	(24.6)
Interest expense	34.6	35.6	67.6	71.2
INCOME BEFORE INCOME TAXES	73.4	77.6	97.1	100.6
Income tax expense (benefit)	48.8	28.0	52.3	36.8
NET INCOME			44.8	63.8
NET INCOME	24.6	49.6	44.8	63.8
Derivative hedging activity
Reclassification to expenses, net of tax	1.0	1.3	1.9	2.6
Derivative hedging activity, net of tax	1.0	1.3	1.9	2.6
Total other comprehensive income	1.0	1.3	1.9	2.6
Comprehensive income (loss)	$ 25.6	$ 50.9	$ 46.7	$ 66.4