Pension Plans and Other Employee Benefits (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Amounts recognized in the consolidated balance sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities		$ (3.4)	$ (2.8)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent		(455.2)	(508.6)
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Unfunded accumulated benefit obligation for GMO SERP		22.9
Segregated assets for GMO SERP		16.4
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan		10.6	9.7	$ 9.6
Kansas City Power and Light Company [Member]
Amounts recognized in the consolidated balance sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities		(2.0)	(1.5)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent		(433.4)	(485.4)
Employee Savings Plans [Abstract]
Defined contribution savings plan, cost of plan		7.9	7.1	7.0
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation		1,186.8	1,007.4
Defined Benefit Plan, Service Cost		45.3	36.7	41.2
Defined Benefit Plan, Interest Cost		50.3	50.1	47.2
Defined Benefit Plan, Contributions by Plan Participants		0.0	0.0
Defined Benefit Plan, Plan Amendments		0.0	0.0
Actuarial (gain) loss		(59.4)	181.1
Defined Benefit Plan, Benefits Paid		(68.2)	(49.0)
Defined Benefit Plan, Settlements, Benefit Obligation		0.0	(39.5)
Defined Benefit Plan, Benefit Obligation		1,154.8	1,186.8	1,007.4
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year		730.0	703.0
Actual return on plan assets		(16.3)	47.2
Defined benefit plan, contributions by employer and participants		76.9	66.2
Defined benefit plan benefits paid portion paid from plan assets		(66.7)	(46.9)
Defined Benefit Plan, Settlements, Plan Assets		0.0	(39.5)
Fair value of plan assets at end of the year		723.9	730.0	703.0
Funded status at end of year		(430.9)	(456.8)
Amounts recognized in the consolidated balance sheets [Abstract]
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent		0.0	0.0
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities		(2.6)	(1.9)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent		(428.3)	(454.9)
Defined Benefit Plan Amounts Recognized in Balance Sheet before Regulatory Treatment		(430.9)	(456.8)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability		461.2	500.5
Defined Benefit Plan, Amounts Recognized in Balance Sheet		30.3	43.7
Amounts in accumulated other comprehensive income or regulatory asset/liability not yet recognized as a component of net periodic benefit cost [Abstract]
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Gains/Losses Before Tax		230.7	273.5
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Prior Service Cost Credit Before Tax		3.9	4.7
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Transition Obligation Before Tax		0.0	0.0
Defined Benefit Plan Accumulated Other Comprehensive Income Other Before Tax		226.6	222.3
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability		461.2	500.5
Components of net periodic benefit costs [Abstract]
Defined Benefit Plan, Service Cost		45.3	36.7	41.2
Defined Benefit Plan, Interest Cost		50.3	50.1	47.2
Defined Benefit Plan, Expected Return on Plan Assets		(51.7)	(50.2)	(47.1)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		0.8	0.9	2.0
Defined Benefit Plan, Amortization of (Gains) Losses		51.4	50.0	54.3
Defined Benefit Plan, Amortization of Transition Obligations (Assets)		0.0	0.0	0.0
Settlement charges		0.0	8.5	4.9
Net periodic benefit costs before regulatory adjustment		96.1	96.0	102.5
Defined Benefit Plan, Regulatory Adjustment		(9.8)	(11.3)	(16.8)
Defined Benefit Plan, Net Periodic Benefit Cost		86.3	84.7	85.7
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Net (gain) loss arising during period		8.6	175.8	(147.0)
Amortization of net gains (losses) included in net periodic benefit costs		(51.4)	(50.0)	(54.3)
Prior service cost		0.0	0.0	0.3
Amortization of prior service cost		(0.8)	(0.9)	(2.0)
Amortization of transition obligation		0.0	0.0	0.0
Other regulatory activity		4.3	7.3	11.8
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability		(39.3)	132.2	(191.2)
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability		47.0	216.9	(105.5)
Estimated prior service cost that will be amortized in the next fiscal year		0.7
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year		$ 51.8
Length Of Time For Amortization Of Net Actuarial Gains And Losses For Financial Reporting Purposes		rolling five-year average
Length Of Time For Amortization Of Net Actuarial Gains And Losses For Regulatory Reporting Purposes		ten years
Accumulated benefit obligation (ABO) for all defined benefit plans		$ 1,017.6	1,036.8
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation		1,154.8	1,186.8
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets		723.9	730.0
Pension plans with the accumulated benefit obligation in excess of plans assets [Abstract]
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation		1,017.6	1,036.8
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets		$ 723.9	$ 730.0
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.54%	4.22%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.62%	3.62%
Defined Benefit Plan, Assumptions Used in Calculations, Narrative Description		The expected long-term rate of return on plan assets represents Great Plains Energy's estimate of the long-term return on plan assets and is based on historical and projected rates of return for current and planned asset classes in the plans' investment portfolios. Assumed projected rates of return for each asset class were selected after analyzing historical experience and future expectations of the returns of various asset classes. Based on the target asset allocation for each asset class, the overall expected rate of return for the portfolios was developed and adjusted for the effect of projected benefits paid from plan assets and future plan contributions.
Weighted average assumptions used to determine net costs [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.22%	5.03%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets		7.14%	7.24%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		3.62%	3.69%
Contribute to plans in next year		$ 75.7
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		81.2
Defined Benefit Plan, Expected Future Benefit Payments, Year Two		77.2
Defined Benefit Plan, Expected Future Benefit Payments, Year Three		77.4
Defined Benefit Plan, Expected Future Benefit Payments, Year Four		80.5
Defined Benefit Plan, Expected Future Benefit Payments, Year Five		82.5
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter		$ 427.3
Defined Benefit Plan, Target Allocation Percentage		The portfolios are invested, and periodically rebalanced, to achieve targeted allocations of approximately 33% U.S. large cap and small cap equity securities, 20% international equity securities, 35% fixed income securities, 7% real estate, 1% commodities and 4% hedge funds.
Defined Benefit Plan, Investment Strategies, Investment Fund Category		The investment strategy supports the objective of the fund, which is to earn the highest possible return on plan assets within a reasonable and prudent level of risk.
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Defined Benefit Plan, Benefit Obligation		$ 165.2	$ 160.5
Defined Benefit Plan, Service Cost		3.3	3.7	4.4
Defined Benefit Plan, Interest Cost		6.8	7.9	7.7
Defined Benefit Plan, Contributions by Plan Participants		6.9	6.8
Defined Benefit Plan, Plan Amendments		(7.1)	0.0
Actuarial (gain) loss		(23.6)	(0.3)
Defined Benefit Plan, Benefits Paid		(14.0)	(13.4)
Defined Benefit Plan, Settlements, Benefit Obligation		0.0	0.0
Defined Benefit Plan, Benefit Obligation		137.5	165.2	160.5
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of the year		110.6	101.2
Actual return on plan assets		(0.1)	4.1
Defined benefit plan, contributions by employer and participants		17.6	18.6
Defined benefit plan benefits paid portion paid from plan assets		(13.8)	(13.3)
Defined Benefit Plan, Settlements, Plan Assets		0.0	0.0
Fair value of plan assets at end of the year		114.3	110.6	101.2
Funded status at end of year		(23.2)	(54.6)
Amounts recognized in the consolidated balance sheets [Abstract]
Defined Benefit Plan, Assets for Plan Benefits, Noncurrent		4.5	0.0
Pension and Other Postretirement Defined Benefit Plans, Current Liabilities		(0.8)	(0.9)
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent		(26.9)	(53.7)
Defined Benefit Plan Amounts Recognized in Balance Sheet before Regulatory Treatment		(23.2)	(54.6)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability		(9.4)	26.1
Defined Benefit Plan, Amounts Recognized in Balance Sheet		(32.6)	(28.5)
Amounts in accumulated other comprehensive income or regulatory asset/liability not yet recognized as a component of net periodic benefit cost [Abstract]
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Gains/Losses Before Tax		(3.3)	17.5
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Prior Service Cost Credit Before Tax		3.4	13.5
Defined Benefit Plan Accumulated Other Comprehensive Income Or Regulatory Asset/Liability Net Transition Obligation Before Tax		0.0	0.2
Defined Benefit Plan Accumulated Other Comprehensive Income Other Before Tax		(9.5)	(5.1)
Defined benefit plan amount recognized in Accumulated Other Comprehensive Income or regulatory asset/liability		(9.4)	26.1
Components of net periodic benefit costs [Abstract]
Defined Benefit Plan, Service Cost		3.3	3.7	4.4
Defined Benefit Plan, Interest Cost		6.8	7.9	7.7
Defined Benefit Plan, Expected Return on Plan Assets		(2.9)	(2.6)	(2.0)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)		3.1	3.1	7.2
Defined Benefit Plan, Amortization of (Gains) Losses		0.2	(0.1)	1.7
Defined Benefit Plan, Amortization of Transition Obligations (Assets)		0.2	0.2	0.2
Settlement charges		0.0	0.0	0.0
Net periodic benefit costs before regulatory adjustment		10.7	12.2	19.2
Defined Benefit Plan, Regulatory Adjustment		4.4	4.3	(2.4)
Defined Benefit Plan, Net Periodic Benefit Cost		15.1	16.5	16.8
Other Changes In Plan Assets And Benefit Obligations Recognized In Other Comprehensive Income Regulatory Assets/Liabilities [Abstract]
Net (gain) loss arising during period		(20.6)	(1.8)	(22.1)
Amortization of net gains (losses) included in net periodic benefit costs		(0.2)	0.1	(1.7)
Prior service cost		(7.0)	0.0	(6.0)
Amortization of prior service cost		(3.1)	(3.1)	(7.2)
Amortization of transition obligation		(0.2)	(0.2)	(0.2)
Other regulatory activity		(4.4)	(4.2)	2.1
Total Recognized In Other Comprehensive Income Or Regulatory Asset/Liability		(35.5)	(9.2)	(35.1)
Total Recognized In Net Periodic Benefit Costs And Other Comprehensive Income Or Regulatory Asset/Liability		(20.4)	7.3	$ (18.3)
Estimated prior service cost that will be amortized in the next fiscal year		1.2
Net (gain) loss for the defined benefit plans that will be amortized in the next fiscal year		(1.5)
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets [Abstract]
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation		108.5	165.2
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets		$ 80.8	$ 110.6
Weighted average assumptions used to determine the benefit obligation [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		4.47%	4.14%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase		3.50%	3.50%
Weighted average assumptions used to determine net costs [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate		4.14%	4.92%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	[1]	2.81%	2.70%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Rate of Compensation Increase		3.50%	3.50%
Contribute to plans in next year		$ 5.1
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		8.2
Defined Benefit Plan, Expected Future Benefit Payments, Year Two		8.8
Defined Benefit Plan, Expected Future Benefit Payments, Year Three		9.5
Defined Benefit Plan, Expected Future Benefit Payments, Year Four		10.2
Defined Benefit Plan, Expected Future Benefit Payments, Year Five		10.8
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter		$ 60.4
Defined Benefit Plan, Investment Strategies, Investment Fund Category		The investment strategy supports the objective of the funds, which is to preserve capital, maintain sufficient liquidity and earn a consistent rate of return.
Health care cost trend (in hundredths)		6.80%	7.00%
Health care cost rate declining through		2025
Ultimate cost trend rate (in hundredths)		4.50%	4.50%
Effect on total service and interest component, increase		$ 0.9
Effect on total service and interest component, decrease		(1.1)
Effect on post-retirement benefit obligation, increase		4.0
Effect on post-retirement benefit obligation, decrease		$ (3.6)

[1] after tax