Revenue from Contract with Customer - Real Estate Services (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 15,081	$ 14,837	$ 14,972
Revenues	20,952	19,844	19,787
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenues	5,396	4,473	4,214
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	475	534	601
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Revenues	5,396	4,473	4,214
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,520	4,028	3,882
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	76	68	67
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,596	4,096	3,949
Revenues	5,396	4,473	4,214
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 800	$ 377	$ 265