Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended			9 Months Ended				9 Months Ended				9 Months Ended		9 Months Ended				9 Months Ended				9 Months Ended		9 Months Ended				9 Months Ended		9 Months Ended				9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		1 Months Ended			1 Months Ended			9 Months Ended				9 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014 Kansas City Power and Light Company [Member]	Sep. 30, 2013 Kansas City Power and Light Company [Member]	Dec. 31, 2013 Kansas City Power and Light Company [Member]	Sep. 30, 2014 Kansas City Power and Light Company [Member] Secured Debt [Member] General Mortgage bonds EIRR due 2015-2035 [Member]		Dec. 31, 2013 Kansas City Power and Light Company [Member] Secured Debt [Member] General Mortgage bonds EIRR due 2015-2035 [Member]		Sep. 30, 2014 Kansas City Power and Light Company [Member] Secured Debt [Member] General Mortgage bonds Series 2009A due 2019 [Member]		Dec. 31, 2013 Kansas City Power and Light Company [Member] Secured Debt [Member] General Mortgage bonds Series 2009A due 2019 [Member]		Sep. 30, 2014 Kansas City Power and Light Company [Member] Secured Debt [Member] General Mortgage bonds EIRR series 2005 due 2035 [Member]	Dec. 31, 2013 Kansas City Power and Light Company [Member] Secured Debt [Member] General Mortgage bonds EIRR series 2005 due 2035 [Member]	Sep. 30, 2014 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior notes due 2017 KCPL [Member]		Dec. 31, 2013 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior notes due 2017 KCPL [Member]		Sep. 30, 2014 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior notes due 2018 KCPL [Member]		Dec. 31, 2013 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior notes due 2018 KCPL [Member]		Sep. 30, 2014 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior Notes due 2023 KCPL [Member]	Dec. 31, 2013 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior Notes due 2023 KCPL [Member]	Sep. 30, 2014 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior notes due 2035 KCPL [Member]		Dec. 31, 2013 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior notes due 2035 KCPL [Member]		Sep. 30, 2014 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior Notes Due 2041 KCPL [Member]	Dec. 31, 2013 Kansas City Power and Light Company [Member] Senior Notes [Member] Senior Notes Due 2041 KCPL [Member]	Sep. 30, 2014 Kansas City Power and Light Company [Member] Unsecured Debt [Member] EIRR Bonds Series 2007A and 2007B due 2035 [Member]		Dec. 31, 2013 Kansas City Power and Light Company [Member] Unsecured Debt [Member] EIRR Bonds Series 2007A and 2007B due 2035 [Member]		Sep. 30, 2014 Kansas City Power and Light Company [Member] Unsecured Debt [Member] EIRR bonds 2.875 percent Series 2008 [Member]	Dec. 31, 2013 Kansas City Power and Light Company [Member] Unsecured Debt [Member] EIRR bonds 2.875 percent Series 2008 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Secured Debt [Member] First Mortgage Bonds due through 2021 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Secured Debt [Member] First Mortgage Bonds due through 2021 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior notes 8.27 percent series due 2021 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior notes 8.27 percent series due 2021 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior Notes Series A due 2025 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior Notes Series A due 2025 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior Notes Series B due 2033 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior Notes Series B due 2033 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior Notes Series C due 2043 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Senior Notes [Member] Senior Notes Series C due 2043 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Medium-term Notes [Member] Medium term notes 7.33 percent series due 2023 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Medium-term Notes [Member] Medium term notes 7.33 percent series due 2023 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Medium-term Notes [Member] Medium term notes 7.17 percent series due 2023 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Medium-term Notes [Member] Medium term notes 7.17 percent series due 2023 [Member]	Jan. 31, 2014 KCPL Greater Missouri Operations [Member] Unsecured Debt [Member] Pollution control bonds Wamego Series 1996 due 2026 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Unsecured Debt [Member] Pollution control bonds Wamego Series 1996 due 2026 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Unsecured Debt [Member] Pollution control bonds Wamego Series 1996 due 2026 [Member]	Jan. 31, 2014 KCPL Greater Missouri Operations [Member] Unsecured Debt [Member] Pollution control bonds state environmental 1993 due 2028 [Member]	Sep. 30, 2014 KCPL Greater Missouri Operations [Member] Unsecured Debt [Member] Pollution control bonds state environmental 1993 due 2028 [Member]	Dec. 31, 2013 KCPL Greater Missouri Operations [Member] Unsecured Debt [Member] Pollution control bonds state environmental 1993 due 2028 [Member]	Sep. 30, 2014 Parent Company [Member] Senior Notes [Member] Senior notes due 2017 [Member]		Dec. 31, 2013 Parent Company [Member] Senior Notes [Member] Senior notes due 2017 [Member]		Sep. 30, 2014 Parent Company [Member] Senior Notes [Member] Senior Notes Due 2021 [Member]	Dec. 31, 2013 Parent Company [Member] Senior Notes [Member] Senior Notes Due 2021 [Member]	Sep. 30, 2014 Parent Company [Member] Senior Notes [Member] Senior Notes Due 2022 [Member]	Dec. 31, 2013 Parent Company [Member] Senior Notes [Member] Senior Notes Due 2022 [Member]	Sep. 30, 2014 Other Consolidated Entities [Member]	Dec. 31, 2013 Other Consolidated Entities [Member]
Debt Instrument [Line Items]
Principal outstanding							$ 146.4	[1]	$ 146.4	[1]	$ 400.0	[2]	$ 400.0	[2]	$ 50.0	$ 50.0	$ 250.0	[2]	$ 250.0	[2]	$ 350.0	[2]	$ 350.0	[2]	$ 300.0	$ 300.0	$ 250.0	[2]	$ 250.0	[2]	$ 400.0	$ 400.0	$ 146.5	[3]	$ 146.5	[3]	$ 23.4	$ 23.4	$ 7.9	$ 9.0	$ 80.9	$ 80.9	$ 125.0	$ 125.0	$ 75.0	$ 75.0	$ 150.0	$ 150.0	$ 3.0	$ 3.0	$ 7.0	$ 7.0		$ 0	$ 7.3		$ 0	$ 5.0	$ 100.0	[2]	$ 100.0	[2]	$ 350.0	$ 350.0	$ 287.5	$ 287.5
Debt Instrument, Maturity Date											Dec. 31, 2019				Dec. 31, 2035		Dec. 31, 2017				Dec. 31, 2018				Dec. 31, 2023		Dec. 31, 2035				Dec. 31, 2041		Dec. 31, 2035				Dec. 31, 2038				Dec. 31, 2021		Dec. 31, 2025		Dec. 31, 2033		Dec. 31, 2043		Dec. 31, 2023		Dec. 31, 2023								Dec. 31, 2017				Dec. 31, 2021		Dec. 31, 2022
Current maturities	(15.1)		(1.1)	(14.0)		0																																																													(1.1)	(1.1)
Unamortized discount				(3.9)		(4.1)
Unarmortized discount and premium, net																																																																			4.5	4.9
Long-term debt excluding current maturities	3,488.1		3,515.7	2,298.4		2,312.2
Debt Instrument Maturity Date Range Start							Dec. 31, 2015																																Dec. 31, 2015
Debt Instrument Maturity Date Range End							Dec. 31, 2035																																Dec. 31, 2021
Interest rates (in hundredths)											7.15%				4.65%		5.85%				6.375%				3.15%		6.05%				5.30%						2.875%		9.44%		8.27%		3.49%		4.06%		4.74%		7.33%		7.17%								6.875%				4.85%		5.292%
Long-term Debt, Weighted Average Interest Rate							2.95%
Variable rate (in hundredths)																																	0.05%
Rate after amortizing gains or losses in Other Comprehensive Income (in hundredths)											8.59%						5.72%				7.49%						5.78%																																7.33%
Repayments of Long-term Debt	$ 13.4	$ 259.3		$ 0	$ 2.6																																																$ 7.3			$ 5.0

[1] Weighted-average interest rates at September 30, 2014

[2] Rate after amortizing gains/losses recognized in OCI on settlements of interest rate hedging instruments

[3] Variable rate