Description of Business and Significant Accounting Policies - Effect of Adoption of ASU 2016-02 As Reported (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
New Accounting Pronouncement, Early Adoption [Line Items]
Operating lease right-of-use asset	$ 60	$ 0
Operating lease liabilities	17	0
Operating lease liabilities, noncurrent	55	0
Accumulated deficit	(229)	$ (266)
Balance Using Previous Standard
New Accounting Pronouncement, Early Adoption [Line Items]
Operating lease right-of-use asset	0
Operating lease liabilities	0
Operating lease liabilities, noncurrent	11
Accumulated deficit	0
Accounting Standards Update 2016-02 | Increase (Decrease)
New Accounting Pronouncement, Early Adoption [Line Items]
Operating lease right-of-use asset	60
Operating lease liabilities	17
Operating lease liabilities, noncurrent	44
Accumulated deficit	$ (229)