Summary of Significant Accounting Standards and Policies - ASU 2016-02 (Details) - USD ($) $ in Millions	Jan. 01, 2019	Sep. 30, 2019
Recently Adopted Accounting Standards
Lease, Practical expedients, Package	true
Lease, Practical expedients, Use of hindsight	false
Operating lease liabilities		$ 141
Operating lease assets		$ 132
ASU 2016-02, Leases
Recently Adopted Accounting Standards
Change in Accounting Principle, Accounting Standards Update, Adopted	true
Change in Accounting Principle, Accounting Standards Update, Transition Option Elected	Modified Retrospective
ASU 2016-02, Leases | Adjustment
Recently Adopted Accounting Standards
Operating lease liabilities	$ 170
Operating lease assets	$ 161