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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 3,317	$ 3,429	$ 6,833	$ 7,116
Operating revenue	4,612	4,894	9,139	9,504
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,193	1,327	2,086	2,112
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	102	138	220	276
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,193	1,327	2,086	2,112
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	957	1,204	1,734	1,915
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	972	1,223	1,765	1,948
Operating revenue	1,193	1,327	2,086	2,112
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	15	19	31	33
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 221	$ 104	$ 321	$ 164