Subsequent event (Details) $ in Millions	Jun. 28, 2018 USD ($)
Premise Health \| Subsequent Event
Subsequent Event [Line Items]
Gain on disposition of minority equity interest	$ 272

Amount of gain (loss) on sale or disposal of equity in securities of subsidiaries.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (13)(g)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

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