Revenue from Contracts with Customers - Real Estate Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Total Customer Revenue	$ 4,712	$ 3,516
Operating revenue	6,081	4,527
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,232	893
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	137	118
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,232	893
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1,022	777
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Total Customer Revenue	18	16
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Total Customer Revenue	1,040	793
Operating revenue	1,232	893
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 192	$ 100