Consolidated Statements of Cash Flows - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
CASH FLOWS FROM (USED IN) OPERATING ACTIVITIES:
Net income	$ 167,300,000	$ 139,500,000
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	217,700,000	182,700,000
Amortization of nuclear fuel	13,700,000	15,900,000
Amortization of deferred refueling outage	8,300,000	8,100,000
Amortization of deferred regulatory gain from sale leaseback	(2,700,000)	(2,700,000)
Amortization of corporate-owned life insurance	9,200,000	8,900,000
Non-cash compensation	20,000,000	4,600,000
Net deferred income taxes and credits	(45,000,000)	53,900,000
Allowance for equity funds used during construction	(1,700,000)	(800,000)
Payments for asset retirement obligations	(8,200,000)	(1,400,000)
Equity in earnings of equity method investees, net of income taxes	(2,700,000)	(3,300,000)
Other	(400,000)	(1,500,000)
Changes in working capital items:
Accounts receivable	(24,700,000)	14,200,000
Accounts receivable pledged as collateral	(15,000,000)	0
Fuel inventory and supplies	25,500,000	(2,300,000)
Prepaid expenses and other current assets	(29,200,000)	37,000,000
Accounts payable	(41,700,000)	(20,000,000)
Accrued taxes	67,800,000	11,000,000
Other current liabilities	(1,600,000)	(103,300,000)
Changes in other assets	(17,300,000)	15,600,000
Changes in other liabilities	57,900,000	7,600,000
Cash Flows from Operating Activities	397,200,000	363,700,000
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Additions to property, plant and equipment	(435,200,000)	(383,600,000)
Cash acquired from the merger with Great Plains Energy	1,154,200,000	0
Purchase of securities - trusts	(96,000,000)	(12,100,000)
Sale of securities - trusts	101,100,000	13,500,000
Investment in corporate-owned life insurance	(15,900,000)	(15,800,000)
Proceeds from investment in corporate-owned life insurance	4,700,000	1,700,000
Proceeds from settlement of interest rate swap	140,600,000	0
Other investing activities	(6,600,000)	(3,200,000)
Cash Flows used in Investing Activities	846,900,000	(399,500,000)
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Short term debt, net	242,600,000	(37,600,000)
Collateralized short-term debt, net	15,000,000	0
Proceeds from long-term debt	0	296,300,000
Retirements of long-term debt	0	(125,000,000)
Repayment of capital leases	(1,900,000)	(1,700,000)
Borrowings against cash surrender value of corporate-owned life insurance	53,900,000	52,300,000
Repayment of borrowings against cash surrender value of corporate-owned life insurance	(3,000,000)	0
Issuance of common stock	0	600,000
Distributions to shareholders of noncontrolling interests	0	(5,800,000)
Cash dividends paid	(228,300,000)	(109,400,000)
Other financing activities	(17,200,000)	(7,000,000)
Cash Flows (used in) from Financing Activities	32,600,000	35,900,000
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	1,276,700,000	100,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH:
Beginning of period	3,500,000	3,200,000
End of period	1,280,200,000	3,300,000
Westar Energy Inc [Member]
CASH FLOWS FROM (USED IN) OPERATING ACTIVITIES:
Net income	140,500,000	139,500,000
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	185,700,000	182,700,000
Amortization of nuclear fuel	11,200,000	15,900,000
Amortization of deferred refueling outage	7,300,000	8,100,000
Amortization of deferred regulatory gain from sale leaseback	(2,700,000)	(2,700,000)
Amortization of corporate-owned life insurance	9,200,000	8,900,000
Non-cash compensation	20,000,000	4,600,000
Net deferred income taxes and credits	(57,900,000)	53,900,000
Allowance for equity funds used during construction	(1,700,000)	(800,000)
Payments for asset retirement obligations	(7,200,000)	(1,400,000)
Equity in earnings of equity method investees, net of income taxes	(2,400,000)	(3,300,000)
Other	(1,400,000)	(1,500,000)
Changes in working capital items:
Accounts receivable	(9,300,000)	14,200,000
Fuel inventory and supplies	26,900,000	(2,300,000)
Prepaid expenses and other current assets	(23,200,000)	37,000,000
Accounts payable	2,800,000	(20,000,000)
Accrued taxes	43,600,000	11,000,000
Other current liabilities	(36,900,000)	(103,300,000)
Changes in other assets	2,400,000	15,600,000
Changes in other liabilities	26,800,000	7,600,000
Cash Flows from Operating Activities	333,700,000	363,700,000
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Additions to property, plant and equipment	(367,700,000)	(383,600,000)
Purchase of securities - trusts	(92,500,000)	(12,100,000)
Sale of securities - trusts	98,400,000	13,500,000
Investment in corporate-owned life insurance	(15,900,000)	(15,800,000)
Proceeds from investment in corporate-owned life insurance	4,700,000	1,700,000
Other investing activities	(7,700,000)	(3,200,000)
Cash Flows used in Investing Activities	(380,700,000)	(399,500,000)
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Short term debt, net	212,500,000	(37,600,000)
Proceeds from long-term debt	0	296,300,000
Retirements of long-term debt	0	(125,000,000)
Repayment of capital leases	(1,900,000)	(1,700,000)
Borrowings against cash surrender value of corporate-owned life insurance	53,900,000	52,300,000
Repayment of borrowings against cash surrender value of corporate-owned life insurance	(3,000,000)	0
Issuance of common stock	0	600,000
Distributions to shareholders of noncontrolling interests	0	(5,800,000)
Cash dividends paid	(169,000,000)	(109,400,000)
Other financing activities	(17,200,000)	(7,000,000)
Cash Flows (used in) from Financing Activities	46,800,000	35,900,000
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(200,000)	100,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH:
Beginning of period	3,500,000	3,200,000
End of period	3,300,000	3,300,000
KCPL [Member]
CASH FLOWS FROM (USED IN) OPERATING ACTIVITIES:
Net income	44,800,000	63,800,000
Adjustments to reconcile income to net cash from operating activities:
Depreciation and amortization	137,100,000	133,600,000
Amortization of nuclear fuel	11,200,000.0	15,900,000.0
Amortization of deferred refueling outage	7,100,000	9,100,000
Net deferred income taxes and credits	24,700,000	19,800,000
Allowance for equity funds used during construction	(1,100,000)	(1,700,000)
Payments for asset retirement obligations	(6,300,000)	(8,100,000)
Other	1,500,000	4,400,000
Changes in working capital items:
Accounts receivable	(33,300,000)	(1,300,000)
Fuel inventory and supplies	(100,000)	4,900,000
Prepaid expenses and other current assets	(11,600,000)	(8,700,000)
Accounts payable	(86,300,000)	(90,600,000)
Accrued taxes	75,200,000	56,700,000
Other current liabilities	19,400,000	(2,900,000)
Changes in other assets	10,900,000	40,600,000
Changes in other liabilities	50,700,000	8,000,000
Cash Flows from Operating Activities	243,900,000	243,500,000
CASH FLOWS FROM (USED IN) INVESTING ACTIVITIES:
Additions to property, plant and equipment	(225,200,000)	(193,400,000)
Purchase of securities - trusts	(20,400,000)	(13,600,000)
Sale of securities - trusts	16,200,000	12,000,000
Other investing activities	2,900,000	(400,000)
Cash Flows used in Investing Activities	(226,500,000)	(195,400,000)
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Short term debt, net	154,900,000	38,900,000
Proceeds from long-term debt	296,600,000	296,500,000
Retirements of long-term debt	(350,000,000)	(250,000,000)
Cash dividends paid	(120,000,000)	(132,000,000)
Other financing activities	2,900,000	0
Cash Flows (used in) from Financing Activities	(15,600,000)	(46,600,000)
NET CHANGE IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	1,800,000	1,500,000
CASH, CASH EQUIVALENTS AND RESTRICTED CASH:
Beginning of period	2,200,000	4,500,000
End of period	4,000,000	6,000,000
Variable Interest Entities [Member]
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Retirements of long-term debt	(28,500,000)	(26,800,000)
Variable Interest Entities [Member] | Westar Energy Inc [Member]
CASH FLOWS FROM (USED IN) FINANCING ACTIVITIES:
Retirements of long-term debt	$ (28,500,000)	$ (26,800,000)