Accounting Policies - Related Party Transactions (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Apr. 30, 2016 USD ($)	Sep. 30, 2016 USD ($) state	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) state	Sep. 30, 2015 USD ($)
Related Party Transaction [Line Items]
Amounts of transaction		$ 7	$ 16	$ 29	$ 37
Charitable Contribution to the CVS Foundation	$ 32
Equity Method Investee
Related Party Transaction [Line Items]
Other revenues from transactions with related party		$ 46		$ 116
Heartland Healthcare Services
Related Party Transaction [Line Items]
Number of states pharmacies operated | state		4		4