Employee Incentive Plans (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee Incentive Plans [Abstract]
Compensation costs	$ 101	$ 88	$ 98
Tax benefits	12	25	26
Number of shares of common stock available for award	10,300,000	13,200,000	8,400,000
Assumptions For Fair Value of Options Granted Details [Abstract]
Dividend Yield	0.10%	0.10%	0.10%
Expected Volatility	35.00%	40.00%	40.00%
Risk-free Interest Rate	1.30%	0.70%	0.80%
Expected Option Life	4 years 4 months	4 years 6 months	4 years 6 months
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding - January 1	7,350,000	8,951,000	9,581,000
Options Granted	2,012,000	1,890,000	3,446,000
Options Exercised	(1,869,000)	(3,107,000)	(3,740,000)
Options Expired or canceled	(162,000)	(384,000)	(336,000)
Options outstanding - December 31	7,331,000	7,350,000	8,951,000
Options Exercisable - Number (in thousands)	3,919,000	4,217,000	5,731,000
Share Based Compensation Arrangement By Share Based Payment Award, Options Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted Average Exercise Price - Options Outstanding - January 1	$ 42.24	$ 36.29	$ 33.92
Weighted Average Exercise Price - Options Granted	$ 78.11	$ 58.84	$ 28.29
Weighted Average Exercise Price - Options Exercised	$ 41.29	$ 34.99	$ 22.72
Weighted Average Exercise Price - Options Expired or canceled	$ 64.27	$ 43.86	$ 37.85
Weighted Average Exercise Price - Options Outstanding - December 31	$ 51.84	$ 42.24	$ 36.29
Options Exercisable - Weighted Average Exercise Price	$ 38.11	$ 35.84	$ 34.93
Information For Stock Options Exercised Details [Abstract]
Intrinsic value of options exercised	84	105	95
Cash received for options exercised	76	109	85
Excess tax benefits realized from options exercised	19	23	15
Information for Outstanding Common Stock Options [Abstract]
Options Outstanding - Number (in thousands)	7,331,000	7,350,000	8,951,000
Options Outstanding - Total intrinsic value	374
Options Outstanding - Weighted Average Exercise Price	$ 51.84	$ 42.24	$ 36.29
Options Outstanding - Weighted average remaining contractual life	6 years 9 months 18 days
Options Exercisable - Number (in thousands)	3,919,000	4,217,000	5,731,000
Options Exercisable - Total Intrinsic Value	254
Options Exercisable - Weighted Average Exercise Price	$ 38.11	$ 35.84	$ 34.93
Options Exercisable - Weighted Average Remaining Contractual Life	5 years 2 months 12 days
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Compensation expense related to non-vested share-based awards	32
Period in which compensation expense will be recognized	2 years
Employee Stock Option [Member] \| Minimum [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Award vesting period	1 year
Employee Stock Option [Member] \| Maximum [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Award vesting period	5 years
Stock options excluding HealthSpring rollover options [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Weighted average fair value of options granted under employee incentive plans	$ 23.56	$ 19.84	$ 14.99
Stock options excluding HealthSpring rollover options [Member] \| Maximum [Member]
Assumptions For Fair Value of Options Granted Details [Abstract]
Remaining maturity of traded options	1 year
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Award expiration period	10 years
Restricted Stock Grants And Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Nonvested, Roll Forward
Outstanding - January 1	2,844,000	4,064,000	4,246,000
Awarded	454,000	525,000	1,563,000
Vested	(1,065,000)	(1,480,000)	(1,485,000)
Forfeited	(112,000)	(265,000)	(260,000)
Outstanding - December 31	2,121,000	2,844,000	4,064,000
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding - January 1	$ 41.56	$ 35.00	$ 28.88
Awarded	$ 78.99	$ 59.36	$ 44.37
Vested	$ 32.34	$ 30.24	$ 27.60
Forfeited	$ 52.95	$ 39.46	$ 33.61
Outstanding - December 31	$ 53.59	$ 41.56	$ 35.00
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Fair value of vested equity-based awards	85	94	66
Number of employees holding share based payment awards at the reporting date.	3,400
Compensation expense related to non-vested share-based awards	54
Period in which compensation expense will be recognized	3 years
Restricted Stock Grants And Units [Member] \| Minimum [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Award vesting period	2 years
Restricted Stock Grants And Units [Member] \| Maximum [Member]
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Award vesting period	5 years
Strategic Performance Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Nonvested, Roll Forward
Outstanding - January 1	1,572,000	1,600,000	834,000
Awarded	450,000	616,000	842,000
Vested	(397,000)	(448,000)	0
Forfeited	(78,000)	(196,000)	(76,000)
Outstanding - December 31	1,547,000	1,572,000	1,600,000
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Outstanding - January 1	$ 49.67	$ 41.92	$ 39.45
Awarded	$ 78.50	$ 59.84	$ 44.49
Vested	$ 43.53	$ 36.88	$ 0
Forfeited	$ 58.41	$ 47.52	$ 43.39
Outstanding - December 31	$ 59.20	$ 49.67	$ 41.92
Employee Service Share-based Compensation, Aggregate Disclosures [Abstract]
Performance period for strategic performance shares	3 years
Fair value of vested equity-based awards	57	42	0
Strategic Performance Shares Subject to Market Conditions	50.00%
Strategic Performance Shares Subject to Performance Conditions	50.00%
Number of employees holding share based payment awards at the reporting date.	1,200
Compensation expense related to non-vested share-based awards	$ 32
Period in which compensation expense will be recognized	2 years

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Number of employees holding share based payment awards at the reporting date.

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Percent of executive strategic performance shares that are subject to a market condition - total shareholder return relative to industry peer companies

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Percent of executive strategic performance shares that are subject to a performance condition - revenue growth and cumulative adjusted net income

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The period of time which a traded option of the reporting entity might be outstanding. The volatility of traded options is not used as a component of the expectedvolatility of outstanding share based compensation option awards as the term of these options does not correlate to the expected term of share-based option awards.

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The period of time over which performance is measured to determine achievement for the performance awards.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (f)(2)(iv)

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

+ References

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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-Publisher FASB

-Name Accounting Standards Codification

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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-Publisher FASB

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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-Publisher FASB

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Weighted average price of options that were either forfeited or expired.

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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

+ References

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Number of share options (or share units) exercised during the current period.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

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-Article 5

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