Goodwill and Other Intangibles - Narrative (Details) - USD ($)	3 Months Ended						12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 02, 2018
Goodwill [Line Items]
Cumulative goodwill impairments		$ 6,100,000,000					$ 6,100,000,000	$ 6,100,000,000
Goodwill impairments	$ 0						0	6,149,000,000	$ 181,000,000
Goodwill		78,678,000,000			$ 38,451,000,000		79,749,000,000	78,678,000,000	38,451,000,000
Amortization of intangible assets							2,436,000,000	1,006,000,000	817,000,000
RX Crossroads
Goodwill [Line Items]
Goodwill impairments					46,000,000	$ 135,000,000
Tax Cuts and Jobs Act, Incomplete Accounting, Change in Tax Rate, Deferred Tax Liability, Provisional Income Tax Benefit									47,000,000
Increase in carrying amount of reported unit									47,000,000
Retail/ LTC
Goodwill [Line Items]
Goodwill impairments								6,149,000,000	181,000,000
Goodwill		10,806,000,000			$ 16,632,000,000		10,807,000,000	$ 10,806,000,000	$ 16,632,000,000
Retail/ LTC | Long-Term Care Reporting Unit
Goodwill [Line Items]
Goodwill impairments		$ 2,200,000,000	$ 0	$ 3,900,000,000
Goodwill							$ 431,000,000
Discontinued Operations, Disposed of by Sale | RX Crossroads | Retail/ LTC
Goodwill [Line Items]
Disposal consideration received										$ 725,000,000