Leases - Analysis of lease liability maturities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Finance Leases
2024	$ 44.8
2025	39.5
2026	30.9
2027	728.4
2028	0.0
Thereafter	0.0
Total undiscounted lease payments	843.6
Imputed interest	(123.6)
Total lease liabilities	720.0
Operating Leases
2024	24.1
2025	20.1
2026	15.6
2027	12.4
2028	11.0
Thereafter	20.1
Total undiscounted lease payments	103.3
Imputed interest	(15.6)
Total lease liabilities	87.7
Total
2024	68.9
2025	59.6
2026	46.5
2027	740.8
2028	11.0
2029	20.1
Total undiscounted lease payments	946.9
Imputed interest	(139.2)
Total lease liabilities	$ 807.7	$ 788.2

Lease, Liability

No definition available.

Name:	regn_LeaseLiability
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- Definition

Lease Liability Payment Due Abstract

+ References

No definition available.

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- Definition

Lease, Liability, Payments, Due

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No definition available.

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- Definition

Lease, Liability, to be Paid, after Year Five

+ References

No definition available.

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- Definition

Lease, Liability, to be Paid, Year Five

+ References

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- Definition

Lease, Liability, to be Paid, Year Four

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- Definition

Lease, Liability, to be Paid, Year One

+ References

No definition available.

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- Definition

Lease, Liability, to be Paid, Year Three

+ References

No definition available.

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- Definition

Lease, Liability, to be Paid, Year Two

+ References

No definition available.

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Data Type:	xbrli:monetaryItemType
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- Definition

Lease, Liability, Undiscounted Excess Amount

+ References

No definition available.

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Balance Type:	credit
Period Type:	instant

- References

No definition available.

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Name:	us-gaap_FinanceLeaseLiabilitiesPaymentsDueAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479041/842-20-45-1

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- Definition

Amount of lessee's undiscounted obligation for lease payments for finance lease.

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+ Details

Name:	us-gaap_FinanceLeaseLiabilityPaymentsDue
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- Definition

Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid 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

+ Details

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- Definition

Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payment for finance lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for finance lease.

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Balance Type:	credit
Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease.

+ References

+ Details

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Period Type:	instant

- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease due 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

+ Details

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- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid 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).

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- Definition

Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid 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

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid 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

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Amount of lessee's undiscounted obligation for lease payment for operating lease to be paid 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

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- Definition

Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease.

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479041/842-20-45-1

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