Revenue from Contracts with Customers Revenue from Contracts with Customers - Real Estate Services (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 4,357	$ 4,213	$ 11,190	$ 11,329
Operating revenue	6,193	5,644	15,332	15,148
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,742	1,307	3,828	3,419
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	94	124	314	400
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,742	1,307	3,828	3,419
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,449	1,172	3,183	3,087
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,472	1,192	3,237	3,140
Operating revenue	1,742	1,307	3,828	3,419
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	23	20	54	53
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 270	$ 115	$ 591	$ 279