Revenue from Contracts with Customers Revenue from Contracts with Customers - Real Estate Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 3,516	$ 3,687
Operating revenue	4,527	4,610
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	893	785
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	118	138
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	893	785
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	777	711
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	793	725
Operating revenue	893	785
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	16	14
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 100	$ 60