Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning Balance in AOCI		$ 83.7	$ 184.8	$ (85.1)
Change in Fair Value Recognized in AOCI		(198.5)	340.3	536.8
Commodity
Generation and Marketing Revenues		18,982.3	19,639.5	16,792.0
Interest Rate
Interest Expense		1,806.9	1,396.1	1,199.1
Amortization of Pension and OPEB
Reclassifications from AOCI, before Income Tax (Expense) Benefit		53.8	(537.7)	(337.9)
Income Tax (Expense) Benefit		54.6	5.4	115.5
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit		42.6	(424.7)	(266.9)
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, Net of Tax		16.7	(16.7)	0.0
Net Current Period Other Comprehensive Income (Loss)		(139.2)	(101.1)	269.9
Ending Balance in AOCI		(55.5)	83.7	184.8
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI
Amortization of Pension and OPEB
Income Tax (Expense) Benefit		4.4
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, before Income Tax (Expense) Benefit		21.1
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, Net of Tax		16.7
Cash Flow Hedges [Member] | Commodity [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning Balance in AOCI		223.5	163.7	(60.6)
Change in Fair Value Recognized in AOCI		(175.8)	477.3	488.2
Amortization of Pension and OPEB
Reclassifications from AOCI, before Income Tax (Expense) Benefit		72.2	(528.5)	(334.1)
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit		57.2	(417.5)	(263.9)
Net Current Period Other Comprehensive Income (Loss)		(118.6)	59.8	224.3
Ending Balance in AOCI		104.9	223.5	163.7
Cash Flow Hedges [Member] | Commodity [Member] | Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI
Amortization of Pension and OPEB
Income Tax (Expense) Benefit		0.0
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, before Income Tax (Expense) Benefit		0.0
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, Net of Tax		0.0
Cash Flow Hedges [Member] | Interest Rate [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning Balance in AOCI		0.3	(21.3)	(47.5)
Change in Fair Value Recognized in AOCI		(6.4)	18.4	21.1
Amortization of Pension and OPEB
Reclassifications from AOCI, before Income Tax (Expense) Benefit		(2.4)	4.0	6.5
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit		(2.0)	3.2	5.1
Net Current Period Other Comprehensive Income (Loss)		(8.4)	21.6	26.2
Ending Balance in AOCI		(8.1)	0.3	(21.3)
Cash Flow Hedges [Member] | Interest Rate [Member] | Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI
Amortization of Pension and OPEB
Income Tax (Expense) Benefit		0.0
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, before Income Tax (Expense) Benefit		0.0
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, Net of Tax		0.0
Pension and OPEB [Member] | Amortization of Deferred Costs [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning Balance in AOCI		105.2	115.6	123.7
Change in Fair Value Recognized in AOCI		0.0	0.0	0.0
Amortization of Pension and OPEB
Reclassifications from AOCI, before Income Tax (Expense) Benefit		(16.0)	(13.2)	(10.3)
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit		(12.6)	(10.4)	(8.1)
Net Current Period Other Comprehensive Income (Loss)		(12.6)	(10.4)	(8.1)
Ending Balance in AOCI		92.6	105.2	115.6
Pension and OPEB [Member] | Changes in Funded Status [Member]
Changes in Accumulated Other Comprehensive Income (Loss) by Component
Beginning Balance in AOCI		(245.3)	(73.2)	(100.7)
Change in Fair Value Recognized in AOCI		(16.3)	(155.4)	27.5
Amortization of Pension and OPEB
Reclassifications from AOCI, before Income Tax (Expense) Benefit		0.0	0.0	0.0
Reclassifications from AOCI, Net of Income Tax (Expense) Benefit		0.0	0.0	0.0
Net Current Period Other Comprehensive Income (Loss)		0.4	(172.1)	27.5
Ending Balance in AOCI		(244.9)	(245.3)	(73.2)
Pension and OPEB [Member] | Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI | Amortization of Deferred Costs [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit		0.0
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, before Income Tax (Expense) Benefit		0.0
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, Net of Tax		0.0
Pension and OPEB [Member] | Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI | Changes in Funded Status [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit		4.4
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, before Income Tax (Expense) Benefit		21.1
Reclassification of KPCo Pension and OPEB Regulatory Assets from AOCI, Net of Tax		16.7
Generation and Marketing Revenues [Member]
Commodity
Generation and Marketing Revenues		1,543.3	2,448.9	2,108.3
Reclassifications To Accumulated Other Comprehensive Income [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit			(4.4)
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, before Income Tax			(21.1)
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, Net of Tax			(16.7)
Reclassifications To Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member] | Commodity [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit			0.0
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, before Income Tax			0.0
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, Net of Tax			0.0
Reclassifications To Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member] | Interest Rate [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit			0.0
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, before Income Tax			0.0
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, Net of Tax			0.0
Reclassifications To Accumulated Other Comprehensive Income [Member] | Pension and OPEB [Member] | Amortization of Deferred Costs [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit			0.0
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, before Income Tax			0.0
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, Net of Tax			0.0
Reclassifications To Accumulated Other Comprehensive Income [Member] | Pension and OPEB [Member] | Changes in Funded Status [Member]
Amortization of Pension and OPEB
Income Tax (Expense) Benefit			(4.4)
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, before Income Tax			(21.1)
Reclassifications of KPCo Pension and OPEB Regulatory Assets to AOCI, Net of Tax			(16.7)
Reclassifications from Accumulated Other Comprehensive Income [Member]
Interest Rate
Interest Expense	[1]	(2.4)	4.0	6.5
Amortization of Pension and OPEB
Amortization of Prior Service Cost (Credit)		(21.2)	(21.8)	(19.4)
Amortization of Actuarial (Gains) Losses		5.2	8.6	9.1
Income Tax (Expense) Benefit		11.2	(113.0)	(71.0)
Reclassifications from Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member] | Commodity [Member]
Interest Rate
Interest Expense	[1]	0.0	0.0	0.0
Amortization of Pension and OPEB
Amortization of Prior Service Cost (Credit)		0.0	0.0	0.0
Amortization of Actuarial (Gains) Losses		0.0	0.0	0.0
Income Tax (Expense) Benefit		15.0	(111.0)	(70.2)
Reclassifications from Accumulated Other Comprehensive Income [Member] | Cash Flow Hedges [Member] | Interest Rate [Member]
Interest Rate
Interest Expense	[1]	(2.4)	4.0	6.5
Amortization of Pension and OPEB
Amortization of Prior Service Cost (Credit)		0.0	0.0	0.0
Amortization of Actuarial (Gains) Losses		0.0	0.0	0.0
Income Tax (Expense) Benefit		(0.4)	0.8	1.4
Reclassifications from Accumulated Other Comprehensive Income [Member] | Pension and OPEB [Member] | Amortization of Deferred Costs [Member]
Interest Rate
Interest Expense	[1]	0.0	0.0	0.0
Amortization of Pension and OPEB
Amortization of Prior Service Cost (Credit)		(21.2)	(21.8)	(19.4)
Amortization of Actuarial (Gains) Losses		5.2	8.6	9.1
Income Tax (Expense) Benefit		(3.4)	(2.8)	(2.2)
Reclassifications from Accumulated Other Comprehensive Income [Member] | Pension and OPEB [Member] | Changes in Funded Status [Member]
Interest Rate
Interest Expense	[1]	0.0	0.0	0.0
Amortization of Pension and OPEB
Amortization of Prior Service Cost (Credit)		0.0	0.0	0.0
Amortization of Actuarial (Gains) Losses		0.0	0.0	0.0
Income Tax (Expense) Benefit		0.0	0.0	0.0
Reclassifications from Accumulated Other Comprehensive Income [Member] | Generation and Marketing Revenues [Member]
Commodity
Generation and Marketing Revenues	[1]		0.1	0.7
Reclassifications from Accumulated Other Comprehensive Income [Member] | Generation and Marketing Revenues [Member] | Cash Flow Hedges [Member] | Commodity [Member]
Commodity
Generation and Marketing Revenues	[1]		0.1	0.7
Reclassifications from Accumulated Other Comprehensive Income [Member] | Generation and Marketing Revenues [Member] | Cash Flow Hedges [Member] | Interest Rate [Member]
Commodity
Generation and Marketing Revenues	[1]		0.0	0.0
Reclassifications from Accumulated Other Comprehensive Income [Member] | Generation and Marketing Revenues [Member] | Pension and OPEB [Member] | Amortization of Deferred Costs [Member]
Commodity
Generation and Marketing Revenues	[1]		0.0	0.0
Reclassifications from Accumulated Other Comprehensive Income [Member] | Generation and Marketing Revenues [Member] | Pension and OPEB [Member] | Changes in Funded Status [Member]
Commodity
Generation and Marketing Revenues	[1]		0.0	0.0
Reclassifications from Accumulated Other Comprehensive Income [Member] | Purchased Electricity, Fuel and Other Consumables Used for Electric Generation [Member]
Commodity
Purchased Electricity, Fuel and Other Consumables Used for Electric Generation	[1]	72.2	(528.6)	(334.8)
Reclassifications from Accumulated Other Comprehensive Income [Member] | Purchased Electricity, Fuel and Other Consumables Used for Electric Generation [Member] | Cash Flow Hedges [Member] | Commodity [Member]
Commodity
Purchased Electricity, Fuel and Other Consumables Used for Electric Generation	[1]	72.2	(528.6)	(334.8)
Reclassifications from Accumulated Other Comprehensive Income [Member] | Purchased Electricity, Fuel and Other Consumables Used for Electric Generation [Member] | Cash Flow Hedges [Member] | Interest Rate [Member]
Commodity
Purchased Electricity, Fuel and Other Consumables Used for Electric Generation	[1]	0.0	0.0	0.0
Reclassifications from Accumulated Other Comprehensive Income [Member] | Purchased Electricity, Fuel and Other Consumables Used for Electric Generation [Member] | Pension and OPEB [Member] | Amortization of Deferred Costs [Member]
Commodity
Purchased Electricity, Fuel and Other Consumables Used for Electric Generation	[1]	0.0	0.0	0.0
Reclassifications from Accumulated Other Comprehensive Income [Member] | Purchased Electricity, Fuel and Other Consumables Used for Electric Generation [Member] | Pension and OPEB [Member] | Changes in Funded Status [Member]
Commodity
Purchased Electricity, Fuel and Other Consumables Used for Electric Generation	[1]	$ 0.0	$ 0.0	$ 0.0

[1] Amounts reclassified to the referenced line item on the statements of income.