Business Combinations - Intangible Assets Identified (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Remainder of 2016		$ 25
2017		25
2018		22
2019		18
2020		13
Fair value of intangible assets acquired	$ 34	$ 51
Weighted-average amortization period for intangible assets	5 years 11 months
Contract rights - member list
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Fair value of intangible assets acquired	$ 28
Weighted-average amortization period for intangible assets	5 years
Provider network
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Fair value of intangible assets acquired	$ 6
Weighted-average amortization period for intangible assets	10 years
Health Plans
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Weighted-average amortization period for intangible assets		6 years 5 months
Health Plans \| Contract rights - member list
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Fair value of intangible assets acquired		$ 23
Weighted-average amortization period for intangible assets		5 years
Health Plans \| Provider network
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Fair value of intangible assets acquired		$ 9
Weighted-average amortization period for intangible assets		10 years
Other
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Weighted-average amortization period for intangible assets		4 years 2 months
Other \| Contract licenses
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Fair value of intangible assets acquired		$ 5
Weighted-average amortization period for intangible assets		2 years
Other \| Contract rights - member list
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Fair value of intangible assets acquired		$ 14
Weighted-average amortization period for intangible assets		5 years
Q1 2016 Acquisitions
Amortization of Intangible Assets Acquired by Fiscal Year Maturity
Remainder of 2016	$ 6
2017	6
2018	6
2019	6
2020	6
2021	$ 1

Finite-Lived Intangible Assets, Amortization Expense, Year Six

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- Definition

Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16265-109275

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- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=26713463&loc=d3e16323-109275

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- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of amortization expense for assets, excluding financial assets and goodwill, lacking physical substance with a finite life expected to be recognized during the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- References

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- Definition

Amount of increase in assets, excluding financial assets, lacking physical substance with a definite life, resulting from a business combination.

+ References

No definition available.

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