Goodwill and Other Intangibles - Goodwill (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Balance, beginning of the period		$ 78,678,000,000	$ 38,451,000,000
Segment realignment		0
Purchase accounting adjustments		1,071,000,000
Acquisitions			46,788,000,000
Foreign currency translation adjustments			(14,000,000)
Other		0
Divestiture of RxCrossroads subsidiary			(398,000,000)
Impairments	$ 0	0	(6,149,000,000)	$ (181,000,000)
Balance, end of the period		79,749,000,000	78,678,000,000	38,451,000,000
Pharmacy Services
Goodwill [Roll Forward]
Balance, beginning of the period		23,388,000,000	21,819,000,000
Segment realignment		194,000,000
Purchase accounting adjustments		0
Acquisitions			1,569,000,000
Foreign currency translation adjustments			0
Other		(1,000,000)
Divestiture of RxCrossroads subsidiary			0
Impairments			0
Balance, end of the period		23,581,000,000	23,388,000,000	21,819,000,000
Retail/ LTC
Goodwill [Roll Forward]
Balance, beginning of the period		10,806,000,000	16,632,000,000
Segment realignment		0
Purchase accounting adjustments		0
Acquisitions			735,000,000
Foreign currency translation adjustments			(14,000,000)
Other		1,000,000
Divestiture of RxCrossroads subsidiary			(398,000,000)
Impairments			(6,149,000,000)	(181,000,000)
Balance, end of the period		10,807,000,000	10,806,000,000	16,632,000,000
Health Care Benefits
Goodwill [Roll Forward]
Balance, beginning of the period		44,484,000,000	0
Segment realignment		(194,000,000)
Purchase accounting adjustments		1,071,000,000
Acquisitions			44,484,000,000
Foreign currency translation adjustments			0
Other		0
Divestiture of RxCrossroads subsidiary			0
Impairments			0
Balance, end of the period		$ 45,361,000,000	$ 44,484,000,000	$ 0