Commitments and Contingencies (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Operating Leases, Rent Expense		$ 751	$ 710	$ 608
Undrawn Letters Of Credit		83
Surety Bonds Outstanding		$ 1,300
Payments to be made to Acquire Businesses, Gross	$ 4,300