Segment Information - Revenues by Product Type (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customer [Line Items]
Premiums	$ 29,642	$ 27,214	$ 25,575
Mail order pharmacy revenues	2,536	2,239	1,827
Other	374	373	305
Revenues from external customers	36,666	33,594	31,003
Medical [Member]
Revenue from External Customer [Line Items]
Premiums	22,696	20,709	19,626
Fees	4,107	3,767	3,307
Total premiums and fees	26,803	24,476	22,933
Guaranteed Cost [Member]
Revenue from External Customer [Line Items]
Premiums	4,761	4,600	4,463
Shared Returns [Member]
Revenue from External Customer [Line Items]
Premiums	2,329	2,322	2,292
Stop Loss [Member]
Revenue from External Customer [Line Items]
Premiums	2,701	2,318	1,907
International Health Care [Member]
Revenue from External Customer [Line Items]
Premiums	1,834	1,827	1,752
Dental [Member]
Revenue from External Customer [Line Items]
Premiums	1,392	1,257	1,139
Medicare [Member]
Revenue from External Customer [Line Items]
Premiums	6,142	5,660	5,639
Medicaid [Member]
Revenue from External Customer [Line Items]
Premiums	1,102	515	317
Medicare Part D [Member]
Revenue from External Customer [Line Items]
Premiums	1,589	1,405	1,387
Other Medical [Member]
Revenue from External Customer [Line Items]
Premiums	846	805	730
Disability [Member]
Revenue from External Customer [Line Items]
Total premiums and fees	1,899	1,767	1,616
Life, Accident and Supplemental Health [Member]
Revenue from External Customer [Line Items]
Total premiums and fees	$ 5,054	$ 4,739	$ 4,322

Revenue excluding net investment income and realized investment results.

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- Definition

Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned, plus amount of fees and commissions from financial services and banking activities and correspondent clearing. Includes fees from depositor accounts, credit cards, merchant discounts, and fiduciary and trust activities, guarantee fees, investment advisory, management, and administrative fees, transfer agent fees, and insurance commissions.

+ References

No definition available.

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- Definition

Reflects premiums and fees related to products within the Other Operations segment, plus other income for all products. Other income reflects the sum of all other revenue and income recognized by the entity in the period not otherwise specified in the income statement. Products within the Other Operations segment include corporate-owned life insurance, run-off retirement and run-off reinsurance products.

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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.

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Amount of fees and commissions from financial services and banking activities and correspondent clearing. Includes fees from depositor accounts, credit cards, merchant discounts, and fiduciary and trust activities, guarantee fees, investment advisory, management, and administrative fees, transfer agent fees, and insurance commissions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13)
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Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums earned.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
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Aggregate revenue during the period from the sale of goods in the normal course of business, after deducting returns, allowances and discounts.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
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-Section S99
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