Revenue from Contracts with Customers Revenue from Contracts with Customers - Real Estate Services (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 3,429	$ 3,564	$ 7,116	$ 7,088
Operating revenue	4,894	4,993	9,504	9,433
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,327	1,273	2,112	2,034
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	138	156	276	311
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,327	1,273	2,112	2,034
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,204	1,168	1,915	1,853
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,223	1,187	1,948	1,887
Operating revenue	1,327	1,273	2,112	2,034
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	19	19	33	34
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 104	$ 86	$ 164	$ 147