Collaborations (UCB) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
UCB [Member] \| Research and development expense [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Cost recoveries	$ 56	$ 48	$ 60

Return of or reimbursements received in relation to direct costs and expenses previously paid or incurred.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Name:	us-gaap_RecoveryOfDirectCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration