Leases - Narrative (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2019 USD ($) store	Mar. 31, 2019 USD ($) store	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) store	Sep. 30, 2018 USD ($)
Lessee, Lease, Description [Line Items]
Sale leaseback transaction, net proceeds, investing activities	$ 0		$ 0	$ 5	$ 0
Store rationalization charges	$ 96		$ 0	$ 231	$ 0
Building | Minimum
Lessee, Lease, Description [Line Items]
Lease term				15 years
Building | Maximum
Lessee, Lease, Description [Line Items]
Lease term				25 years
Equipment and other assets | Minimum
Lessee, Lease, Description [Line Items]
Lease term				3 years
Equipment and other assets | Maximum
Lessee, Lease, Description [Line Items]
Lease term				10 years
Retail Long-Term Care Segment
Lessee, Lease, Description [Line Items]
Number of under performing stores | store	22	46		22
Store rationalization charges	$ 96	$ 135