Long-Term Debt Leases and Debt Maturities (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Long-Term Debt
Long-Term Debt, Payments Due in 2021	$ 4.1
Long-Term Debt, Payments Due in 2022	4.3
Long-Term Debt, Payments Due in 2023	649.2
Long-Term Debt, Payments Due in 2024	4.7
Long-Term Debt, Payments Due in 2025	5.1
Long-Term Debt, Payments Due Thereafter	3,143.5
Total Long-Term Debt	3,810.9
Finance Leases, Net Present Value [Abstract]
Finance Leases, Net Present Value, Payments Due in 2021	2.3
Finance Leases, Net Present Value, Payments Due in 2022	2.5
Finance Leases, Net Present Value, Payments Due in 2023	2.4
Finance Leases, Net Present Value, Payments Due in 2024	0.3
Finance Leases, Net Present Value, Payments Due in 2025	0.0
Finance Leases, Net Present Value, Payments Due Thereafter	0.0
Total Finance Leases, Net Present Value	7.5
Long Term Debt And Finance Lease Obligation [Abstract]
Total Debt, Payments Due in 2021	6.4
Total Debt, Payments Due in 2022	6.8
Total Debt, Payments Due in 2023	651.6
Total Debt, Payments Due in 2024	5.0
Total Debt, Payments Due in 2025	5.1
Total Debt, Payments Due Thereafter	3,143.5
Total Debt, Payments Due	$ 3,818.4	$ 3,285.6

Finance Lease, Liability, Net Present Value Payments Due [Abstract]

No definition available.

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueAbstract
Namespace Prefix:	ksu_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Present value of lessee's discounted obligation for lease payments for finance lease, due in next fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueNextTwelveMonths
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments for finance lease, due after fifth fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueThereafter
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments for finance lease, due in fifth fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueYearFive
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments for finance lease, due in fourth fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueYearFour
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments for finance lease, due in third fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueYearThree
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lessee's discounted obligation for lease payments for finance lease, due in second fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_FinanceLeaseLiabilityNPVPaymentsDueYearTwo
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Long Term Debt And Finance Lease Obligation [Abstract]

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationAbstract
Namespace Prefix:	ksu_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of long-term debt and finance lease obligation maturing after the fifth fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationsMaturitiesRepaymentsOfPrincipalDueThereafter
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt and finance lease obligation maturing in the fifth fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationsMaturitiesRepaymentsOfPrincipalDueYearFive
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt and finance lease obligation maturing in the fourth fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationsMaturitiesRepaymentsOfPrincipalDueYearFour
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt and finance lease obligation maturing in the third fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationsMaturitiesRepaymentsOfPrincipalDueYearThree
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt and finance lease obligation maturing in the second fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationsMaturitiesRepaymentsOfPrincipalDueYearTwo
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt and finance lease obligation maturing in the next fiscal year following the current fiscal year.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtAndFinanceLeaseObligationsMaturitiesRepaymentsOfPrincipalNextTwelveMonths
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of long-term debt and finance lease obligations, including current maturities, before unamortized (discount) premium and debt issuance costs.

+ References

No definition available.

+ Details

Name:	ksu_LongTermDebtandFinanceLeaseObligationsIncludingCurrentMaturitiesGross
Namespace Prefix:	ksu_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870

Reference 2: 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=120400017&loc=d3e572229-122910

Reference 3: 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=120391452&loc=d3e13212-122682

Reference 4: 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=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918701-209980

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918627-209977

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing after fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-04.(a))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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

- Definition

Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

+ References

+ Details

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