Contingencies (Health Care Cost Recovery Litigation) (Details) - Health Care Cost Recovery Actions [Member]	1 Months Ended	3 Months Ended
	Nov. 30, 1998 USD ($) state	Mar. 31, 2018 USD ($) case	Mar. 31, 2017 USD ($)	Apr. 27, 2017 case	Apr. 25, 2016 case
Loss Contingencies [Line Items]
Number of cases pending | case				1	1
Number of states with settled litigation | state	46
State Settlement Agreements annual payments	$ 9,400,000,000
State Settlement Agreements attorney fees annual cap	$ 500,000,000
Litigation settlement		$ 1,000,000,000	$ 1,100,000,000
Threatened Litigation [Member] | Canada [Member]
Loss Contingencies [Line Items]
Number of cases pending | case		10