Contingencies (Health Care Cost Recovery - Federal Government's Lawsuit Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Aug. 31, 2006	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2014
Loss Contingencies [Line Items]
Provision related to litigation recorded		$ 12	$ 21	$ 70	$ 28	$ 62	$ 0	$ 17	$ 1
Federal Governments Lawsuit [Member]
Loss Contingencies [Line Items]
Federal trade commission, disclosure period	10 years
Implementation of Corrective Communications [Member] | Federal Governments Lawsuit [Member]
Loss Contingencies [Line Items]
Provision related to litigation recorded										$ 31