Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 36
Operating lease, liabilities	$ 36
ASU 2016-02
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets		$ 34
Operating lease, liabilities		$ 34