Business Acquisitions (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Acquisition, net of cash acquired		$ (106)	$ (1,113)	$ (66)
Goodwill		9,595	9,678	9,010
Business acquisition, acquisition of remaining noncontrolling interest		131	0	0
Other acquisitions [Member]
Business Acquisition [Line Items]
Acquisition, net of cash acquired		(100)	(1,100)	(66)
Total assets assumed		0	1,100
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		12	487	54
Goodwill		$ 79	$ 508	$ 50
HomeServices [Member] | Real estate brokerage franchise business [Member]
Business Acquisition [Line Items]
Ownership Percentage Acquired	33.30%
Business acquisition, acquisition of remaining noncontrolling interest	$ 131