Significant Accounting Policies - Narrative (Details) person in Millions, patient in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) patient clinic state person building	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) patient Segment clinic state person building	Sep. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Significant Accounting Policies [Line Items]
Number of pharmacy plan members | person	103		103
Number of patients served per year | patient	1		1
Number of reportable segments | Segment			4
Allowance for credit losses	$ 363		$ 363				$ 319
Health insurer fee	255		774
Non tax-deductible health insurance fee			1,000
Related party transaction, expenses from transactions with related party	5	$ 14	28	$ 26
Related party transaction, other revenues from transactions with related party	15	20	$ 58	72
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Change in Accounting Principle, Accounting Standards Update, Transition Option Elected [Extensible List]			us-gaap:AccountingStandardsUpdate201615ProspectiveMember
Cumulative adjustment to retained earnings as a result of new accounting standard adoption	$ 69,112	62,933	$ 69,112	62,933	$ 68,355	$ 65,474	64,170	$ 61,599	$ 60,006	$ 58,543
Heartland Healthcare Services
Significant Accounting Policies [Line Items]
Number of states in which entity operates | state	4		4
Retail/ LTC
Significant Accounting Policies [Line Items]
Number of stores | building	9,900		9,900
Number of walk in medical clinics | clinic	1,100		1,100
Health Care Benefits
Significant Accounting Policies [Line Items]
Number of people served through health insurance products and related services | person	33		33
Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative adjustment to retained earnings as a result of new accounting standard adoption	$ 49,328	$ 44,017	$ 49,328	$ 44,017	$ 48,768	$ 46,455	45,108	$ 43,136	$ 41,859	40,911
Cumulative Effect, Period of Adoption, Adjustment
Significant Accounting Policies [Line Items]
Cumulative adjustment to retained earnings as a result of new accounting standard adoption							(3)			178	[1]
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings
Significant Accounting Policies [Line Items]
Cumulative adjustment to retained earnings as a result of new accounting standard adoption							$ (3)			$ 178	[1]

[1] Reflects the adoption of Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842), which resulted in an increase to retained earnings of $178 million during the three months ended March 31, 2019.