Employee Incentive Plans - Strategic Performance Shares (Details) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) Employees $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares
Employee Incentive Plan Aggregate Disclosures [Line Items]
Compensation cost \| $	$ 178	$ 128	$ 111
Strategic Performance Shares [Member]
Employee Incentive Plan Aggregate Disclosures [Line Items]
Performance period	3 years
Percent of shares subject to market conditions	50.00%
Percent of shares subject to performance conditions	50.00%
Compensation cost \| $	$ 40	$ 35	$ 36
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Nonvested, Roll Forward
Outstanding - January 1	942	1,188	1,547
Awarded	275	286	311
Vested	(386)	(494)	(608)
Forfeited	(53)	(38)	(62)
Outstanding - December 31	778	942	1,188
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 \| $ / shares	$ 109.14	$ 81.68	$ 59.2
Awarded \| $ / shares	150.06	139.05	121.78
Vested \| $ / shares	78.91	60.15	45.51
Forfeited \| $ / shares	138.19	112.7	76.33
Outstanding - December 31 \| $ / shares	$ 136.57	$ 109.14	$ 81.68
Employee Service Share-based Compensation, Additional Disclosures [Abstract]
Shares of Cigna common stock distributed upon SPS vesting	476	768	972
Fair value of shares vested \| $	$ 70	$ 109	$ 119
Number of employees holding share-based payment awards \| Employees	1,500
Related compensation expense to be recognized \| $	$ 38
Period over which compensation expense will be recognized	2 years
Strategic Performance Shares [Member] \| Minimum [Member]
Employee Incentive Plan Aggregate Disclosures [Line Items]
Percentage of original shares granted that may be awarded at end of performance period	0.00%
Strategic Performance Shares [Member] \| Maximum [Member]
Employee Incentive Plan Aggregate Disclosures [Line Items]
Percentage of original shares granted that may be awarded at end of performance period	200.00%

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

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The percent of the original grant amount that holders of strategic performance shares will be awarded in shares of the Company's common stock at the end of the performance period.

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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 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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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 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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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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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Number of treasury shares (units) reissued during the period, excluding reissuance of shares (units) held in treasury used to satisfy equity-based compensation obligations exercised by the holders of such rights. Upon reissuance of shares (units) from treasury, either the common or preferred stock (unit) reissued is outstanding.

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