Contingencies and Other Matters - Anthem Litigation (Details) $ in Millions	Dec. 31, 2017 USD ($)
Contingencies And Other Matters [Abstract]
Termination fee payable to Company	$ 1,850
Positive Outcome Of Litigation [Member] \| Minimum [Member]
Gain Contingencies [Line Items]
Damages sought	$ 13,000

The amount or range of possible amounts of gain that could be realized upon the resolution of a contingency.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 30
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6397426&loc=d3e17499-108355

Name:	us-gaap_GainContingencyUnrecordedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant