Basis of Presentation, Uses of Estimates and Significant Accounting Policies (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Accounts payable and accrued liabilities	$ 15,180	$ 13,361
Other current receivables	6,262	7,499
Goodwill, Impairment Loss	0
Impairment of Intangible Assets (Excluding Goodwill)	$ 0
Number Of Days Notice Required To Cancel Health Insurance Contract	30 days
Accounts Receivable, Net, Current	$ 9,568	8,152
Other Liabilities, Current	12,286	10,339
Other Current Liabilities [Member]
Health savings account deposits	$ 6,400	5,700
Restricted Stock [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	2 years
Restricted Stock [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	5 years
Stock Options and SARs [Member] [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Share-based Compensation Arrangement by Share-based Payment Plan Award, Options, Award Exercisable Period	10 years
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Discount from Market Price, Offering Date	85.00%
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Description of Transition Method	Modified Retrospective
New Accounting Pronouncement, Transition Guidance Not Significant or Not Practical	Impact is not material
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncement or Change in Accounting Principle, Description of Transition Method	Modified Retrospective
New Accounting Pronouncement, Transition Guidance Not Significant or Not Practical	Impact is not material
Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncement, Transition Guidance Not Significant or Not Practical	Impact is not material
Health Insurance Product Line [Member]
Short-duration Insurance Contracts, Historical Claims Duration, First 90 Days	0.9
Products and services [Member]
Accounts Receivable, Net, Current	$ 3,700
Pharmaceutical Manufacturer Rebates Receivable [Member]
Other current receivables	3,800	3,300
Medicare Part D Liabilities [Member]
Other Liabilities, Current	1,600	700
Medicare Part D Receivables [Member]
Other current receivables	$ 500	$ 1,500

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