Business Acquisitions - Pro Forma Information (Details) - Aetna Group Insurance - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Revenue	$ 18,899	$ 18,348
Earnings	$ (3,077)	$ 953

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

+ Details

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- Definition

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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- Definition

The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

+ Details

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- Details

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