Investments (Securities Lending Programs) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2020	Dec. 31, 2019
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Loaned, Fair Value of Collateral	$ 1,019	$ 351
Securities Lending Transactions Ratio of Fair Value of Collateral Held To Securities On Loan	102.00%	103.00%
Overnight and Continuous [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral received for securities loaned, at carrying value	$ 1,019
Overnight and Continuous [Member] \| Cash [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral received for securities loaned, at carrying value	898
Overnight and Continuous [Member] \| United States Government Securities [Member]
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Collateral received for securities loaned, at carrying value	$ 121

Ratio of fair value of collateral held to fair value of securities loaned in securities lending transactions.

No definition available.

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Namespace Prefix:	antm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash received as security in return for loaning securities to another party.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04(11))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

+ Details

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- Definition

Fair value of the securities pledged as collateral against securities loaned.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226013-175313

+ Details

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- Definition

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.

+ References

No definition available.

+ Details

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- Details

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- Details

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