Statement of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Accrued capital expenditures	$ 17.6	$ 10.1	$ 16.1	$ 8.6
Facility lease obligation recognized during the period	$ 19.4	$ 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