Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accrued capital expenditures	$ 41.8	$ 28.2	$ 50.7
Facility lease obligations recognized	$ 201.2	$ 154.9	$ 26.0

Carrying value as of the balance sheet date of obligations incurred and payable for purchases of fixed assets. Included in accounts payable and accrued expenses.

No definition available.

Name:	regn_AccruedCapitalExpenditures
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant