Short-term Borrowings and Short-term Bank Lines of Credit (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jul. 31, 2017	Dec. 31, 2016
Short-term Debt [Line Items]
Commercial paper outstanding	$ 424.6		$ 334.8
Great Plains Energy [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200.0
Credit facility expiration date	Oct. 31, 2019
Maximum borrowing capacity with transfer of unused commitments	$ 400.0
Line of Credit Facility, Covenant Terms	A default by Great Plains Energy or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility.  Under the terms of this facility, Great Plains Energy is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		0.0
Amount of letters of credit outstanding	1.0		1.0
Great Plains Energy [Member] | Bridge Loan [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	8,017.0
Amount of bridge facility, as amended	864.5
Great Plains Energy [Member] | Bridge Loan [Member] | Subsequent Event [Member]
Short-term Debt [Line Items]
Amount of bridge facility, as amended		$ 864.5
Kansas City Power and Light Company [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 171.8		$ 132.9
Weighted-average interest rate from outstanding borrowings	1.42%		0.98%
Kansas City Power and Light Company [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 600.0
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200.0
Line of Credit Facility, Covenant Terms	A default by KCP&L on other indebtedness totaling more than $50.0 million is a default under the facility.  Under the terms of this facility, KCP&L is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		$ 0.0
Amount of letters of credit outstanding	2.7		2.8
KCPL Greater Missouri Operations [Member]
Short-term Debt [Line Items]
Commercial paper outstanding	$ 252.8		$ 201.9
Weighted-average interest rate from outstanding borrowings	1.43%		1.02%
KCPL Greater Missouri Operations [Member] | Revolving Credit Facility [Member]
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 450.0
Credit facility expiration date	Oct. 31, 2019
Maximum transfer of unused commitments	$ 200.0
Line of Credit Facility, Covenant Terms	A default by GMO or any of its significant subsidiaries on other indebtedness totaling more than $50.0 million is a default under the facility.  Under the terms of this facility, GMO is required to maintain a consolidated indebtedness to consolidated capitalization ratio, as defined in the facility, not greater than 0.65 to 1.00 at all times.
Line of Credit Facility, Covenant Compliance	in compliance
Amount of outstanding cash borrowings	$ 0.0		$ 0.0
Amount of letters of credit outstanding	$ 2.0		$ 1.9