Revenues (Comparison Of The Reported Condensed Consolidated Statement Of Financial Position To The Pro-forma Amounts Had The Previous Guidance Been In Effect) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables	$ 218	$ 186
Prepaid expenses and other assets	83	61
Deferred customer acquisition costs	95	77
Total Assets	5,322	5,023
Deferred revenue	111	95
Deferred taxes	501	484
Other long-term obligations, primarily self-insured claims	164	182		$ 2,925
Total Liabilities	776	666
Retained earnings	291	156
Accumulated other comprehensive income	9	5	$ 5		$ 7
Revenues	2,077	1,900	1,755
Cost of services rendered and products sold	1,178	1,041	962
Selling and administrative expenses	578	555	500
Provision (benefit) for income taxes	27	37	(242)
Net Income	128	(41)	$ 510
Liabilities and Equity	$ 5,322	5,023
Under Prior Revenue Recognition Guidance [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenues		1,886
Cost of services rendered and products sold		1,041
Selling and administrative expenses		548
Provision (benefit) for income taxes		35
Net Income		(46)
Impact of adopting ASC 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables		186
Prepaid expenses and other assets		61
Deferred customer acquisition costs		77
Total Assets		5,023
Deferred revenue		95
Deferred taxes		484
Other long-term obligations, primarily self-insured claims		182
Total Liabilities		2,818
Retained earnings		156
Accumulated other comprehensive income		5
Revenues		1,900
Cost of services rendered and products sold		1,041
Selling and administrative expenses		555
Provision (benefit) for income taxes		37
Net Income		(41)
Liabilities and Equity		5,023
Impact of adopting ASC 606 [Member] | Under Prior Revenue Recognition Guidance [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Receivables		186
Prepaid expenses and other assets		74
Deferred customer acquisition costs		22
Total Assets		4,982
Deferred revenue		91
Deferred taxes		473
Other long-term obligations, primarily self-insured claims		176
Total Liabilities		2,798
Retained earnings		141
Accumulated other comprehensive income		5
Net Income		(46)
Liabilities and Equity		$ 4,982