Revenue from Contract with Customer Revenue from Contracts with Customers - Real Estate Services (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 14,837	$ 14,972
Revenues	19,844	19,787	$ 18,614
Residential real estate brokerage and mortgage businesses [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,473	4,214	3,443
Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	534	601
HomeServices [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,473	4,214	$ 3,443
HomeServices [Member] | Residential real estate brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,028	3,882
HomeServices [Member] | Real estate franchise [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	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	4,096	3,949
Revenues	4,473	4,214
HomeServices [Member] | Non-contracts with customer revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 377	$ 265