PENSION PLANS AND OTHER EMPLOYEE BENEFITS (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Components of net periodic benefit costs [Abstract]
Contributions made by the Company			$ 42.0
Voluntary Separation Program [Line Items]
Annual Savings In Labor Costs Expected From Voluntary Savings Program	15.0		15.0
Voluntary separation program	0	0	12.7	0
Employees who elected to voluntarily separate (in employees)	140		140
Date of employee separation	Apr. 30, 2011		Apr. 30, 2011
Pension Benefits [Member]
Components of net periodic benefit costs [Abstract]
Service cost	7.8	7.6	23.4	22.8
Interest cost	12.4	12.3	37.5	36.9
Expected return on plan assets	(9.5)	(9.2)	(28.8)	(27.5)
Prior service cost	1.1	1.1	3.4	3.5
Recognized net actuarial loss (gain)	9.7	9.4	28.9	28.1
Transition obligation	0	0	0	0
Settlement charge	10.0	0	10.2	0
Net periodic benefit costs before regulatory adjustment	31.5	21.2	74.6	63.8
Regulatory adjustment	(12.8)	(8.1)	(25.1)	(24.6)
Net periodic benefit costs	18.7	13.1	49.5	39.2
Additional contribution expected in the year	80.2		80.2
Other Benefits [Member]
Components of net periodic benefit costs [Abstract]
Service cost	0.7	1.0	2.3	2.8
Interest cost	2.0	2.2	5.9	6.6
Expected return on plan assets	(0.4)	(0.5)	(1.3)	(1.6)
Prior service cost	1.8	1.8	5.4	5.4
Recognized net actuarial loss (gain)	(0.1)	(0.1)	(0.4)	(0.1)
Transition obligation	0.3	0.3	1.0	1.0
Settlement charge	0	0	0	0
Net periodic benefit costs before regulatory adjustment	4.3	4.7	12.9	14.1
Regulatory adjustment	0.4	0	0.7	0
Net periodic benefit costs	4.7	4.7	13.6	14.1
Additional contribution expected in the year	$ 17.1		$ 17.1

Expected annual savings in labor costs due to the voluntary separation program

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Date that the majority of employees separated from the Company under the voluntary separation program

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The employer's best estimate, as soon as it can be reasonably determined, of contributions expected to be paid to the plan during the remainder of the fiscal year. Estimated contributions may be presented in the aggregate combining (1) contributions required by funding regulations or laws, (2) discretionary contributions, and (3) noncash contributions.

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The total amount of net periodic benefit cost for defined benefit plans for the period before regulatory adjustments.

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Difference between pension costs under GAAP and pension costs for ratemaking purposes. This difference is due to timing and will be eliminated over the life of the pension plans.

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Number of employees who elected to separate from the Company under the voluntary separation program

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Expenses related to Great Plains Energy's organizational realignment process and voluntary separation program undertaken to assist in the management of overall costs within the level reflected in the Company's retial electric rates and to enhance organizational efficiency.

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The amount of gains or losses recognized in net periodic benefit cost

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The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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The amount of the transition obligation or asset recognized in net periodic benefit cost.

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The amount of contributions made by the employer.

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain or loss, prior service cost or credit, transition asset or obligation, and gain or loss due to settlements or curtailments).

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The amount of net (gain) loss recognized in net periodic benefit cost as a result of an irrevocable action that relieves the employer (or the plan) of primary responsibility for a benefit obligation and eliminates significant risks related to the obligation and the assets used to effect the settlement. Examples of transactions that constitute a settlement include (a) making lump-sum cash payments to plan participants in exchange for their rights to receive specified benefits and (b) purchasing nonparticipating annuity contracts to cover vested benefits.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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