Revenue from Contracts with Customers Revenue from Contracts with Customers - Real Estate Services (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 3,687	$ 3,524
Operating revenue	4,610	4,440
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	785	761
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	138	155
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	785	761
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	711	685
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	725	700
Operating revenue	785	761
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	14	15
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 60	$ 61