Supplemental Disclosures (Schedule of Supplemental Cash Flow Disclosures) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Assets acquired, excluding cash	$ 1,100	$ 898	$ 960
Liabilities assumed	(83)	(134)	(111)
Contingent/deferred purchase consideration	(133)	(109)	(36)
Net cash outflow for acquisitions	884	655	813
Interest paid	264	199	178
Income taxes paid, net of refunds	$ 632	$ 583	$ 642