Fair Value Measurements (Details) $ in Millions	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Assets [Abstract]
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4	$ 79.3
Self-insured health plan trust [Abstract]
Fair Value Inputs, Contingency Factor	0.35	0.35
Fair Value, Measurements, Recurring [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4	$ 79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	232.5	222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3	11.3
Total assets	335.2	313.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets [Abstract]
Derivative instruments, assets	0.0	0.0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	195.5	185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.7	6.6
Total assets	204.2	192.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets [Abstract]
Derivative instruments, assets	0.0	0.0
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	37.0	37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.6	4.7
Total assets	39.6	42.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets [Abstract]
Derivative instruments, assets	91.4	79.3
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Total assets	91.4	79.3
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	232.5	222.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	11.3	11.3
Total assets	243.8	234.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	161.7	153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.7	0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.6	4.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	28.2	27.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	1.7	1.7
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.1	3.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	31.1	32.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1	0.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	5.6	3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.0	5.6
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	195.5	185.5
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.7	6.6
Total assets	204.2	192.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	161.7	153.9
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.7	0.9
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	28.2	27.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	5.6	3.8
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 1 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	8.0	5.6
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	37.0	37.4
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.6	4.7
Total assets	39.6	42.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	2.6	4.7
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	1.7	1.7
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	4.1	3.2
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	31.1	32.4
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.1	0.1
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 2 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Total assets	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Securities [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Treasury and Government [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Corporations and Agencies Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | US States and Political Subdivisions Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash Equivalents [Member]
Nuclear decommissioning trust [Abstract]
Decommissioning Fund Investments, Fair Value	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Kansas City Power and Light Company [Member] | Fair Value, Inputs, Level 3 [Member] | Cash and Cash Equivalents [Member]
Self-insured health plan trust [Abstract]
Self Insured Health Plan Trust Fair Value Disclosure	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member]
Self-insured health plan trust [Abstract]
Total assets	91.4	79.3
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	91.4	$ 79.3
Derivatives, Interest Rate Swaps, Finalized Settlement Value	$ 140.6
Self-insured health plan trust [Abstract]
Fair Value Inputs, Contingency Factor	0.35	0.35
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member]
Self-insured health plan trust [Abstract]
Total assets	$ 0.0	$ 0.0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 1 [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member]
Self-insured health plan trust [Abstract]
Total assets	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member]
Self-insured health plan trust [Abstract]
Total assets	91.4	79.3
Fair Value, Measurements, Recurring [Member] | Other Consolidated Entities [Member] | Fair Value, Inputs, Level 3 [Member] | Interest Rate Contract [Member]
Assets [Abstract]
Derivative instruments, assets	$ 91.4	$ 79.3