Business Segment Reporting (Narrative) (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018 customer segment	Dec. 31, 2019 customer segment	Dec. 31, 2018 USD ($) customer	Dec. 31, 2017 USD ($) customer
Business segment reporting [Line Items]
Number of reportable segments | segment	2	2
Maximum percentage of revenue from customers and franchisees generated in foreign market		3.00%
Number of customers exceeding 10 percent of global sales | customer	0	0	0	0
Corporate And Other Operations [Member] | American Home Shield [Member]
Business segment reporting [Line Items]
Other expense | $			$ 33	$ 44