SHORT-TERM BORROWINGS AND SHORT-TERM BANK LINES OF CREDIT - Schedule of Short Term Debt (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Credit Facility	$ 2,500.0	$ 2,500.0
Available Borrowings	1,664.9	1,737.3
Evergy, Inc.
Short-term Debt [Line Items]
Credit Facility	450.0	450.0
Available Borrowings	$ 349.0	$ 449.0
Weighted Average Interest Rate on Short-Term Borrowings	3.73%	0.00%
Westar Energy
Short-term Debt [Line Items]
Credit Facility	$ 1,000.0	$ 1,000.0
Available Borrowings	$ 567.9	$ 570.0
Weighted Average Interest Rate on Short-Term Borrowings	2.77%	3.08%
KCP&L
Short-term Debt [Line Items]
Credit Facility	$ 600.0	$ 600.0
Available Borrowings	$ 421.3	$ 420.4
Weighted Average Interest Rate on Short-Term Borrowings	2.89%	2.95%
GMO
Short-term Debt [Line Items]
Credit Facility	$ 450.0	$ 450.0
Available Borrowings	$ 326.7	$ 297.9
Weighted Average Interest Rate on Short-Term Borrowings	2.75%	3.00%
Commercial Paper
Short-term Debt [Line Items]
Long-term line of credit	$ 711.0	$ 738.6
Commercial Paper \| Westar Energy
Short-term Debt [Line Items]
Long-term line of credit	413.8	411.7
Commercial Paper \| KCP&L
Short-term Debt [Line Items]
Long-term line of credit	176.0	176.9
Commercial Paper \| GMO
Short-term Debt [Line Items]
Long-term line of credit	121.2	150.0
Letters of Credit
Short-term Debt [Line Items]
Letters of Credit	24.1	24.1
Letters of Credit \| Evergy, Inc.
Short-term Debt [Line Items]
Letters of Credit	1.0	1.0
Letters of Credit \| Westar Energy
Short-term Debt [Line Items]
Letters of Credit	18.3	18.3
Letters of Credit \| KCP&L
Short-term Debt [Line Items]
Letters of Credit	2.7	2.7
Letters of Credit \| GMO
Short-term Debt [Line Items]
Letters of Credit	2.1	2.1
Cash Borrowings
Short-term Debt [Line Items]
Long-term line of credit	100.0	0.0
Cash Borrowings \| Evergy, Inc.
Short-term Debt [Line Items]
Long-term line of credit	100.0	0.0
Cash Borrowings \| Westar Energy
Short-term Debt [Line Items]
Long-term line of credit	0.0	0.0
Cash Borrowings \| KCP&L
Short-term Debt [Line Items]
Long-term line of credit	0.0	0.0
Cash Borrowings \| GMO
Short-term Debt [Line Items]
Long-term line of credit	$ 0.0	$ 0.0

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The effective interest rate at the end of the reporting period.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_ShortTermDebtLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	dei_LegalEntityAxis=evrg_EvergyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=evrg_WestarEnergyIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=evrg_KCPLMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=evrg_KcplGreaterMissouriOperationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_CommercialPaperMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: