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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 4,270		$ 11,358
Operating revenue	5,637	$ 5,283	15,070	$ 14,003
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,218	961	3,252	2,502
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	149		460
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	1,218	$ 961	3,252	$ 2,502
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,122		2,975
HomeServices [Member] | Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,140		3,027
Operating revenue	1,218		3,252
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	18		52
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Operating revenue	$ 78		$ 225