Summary of Significant Accounting Policies - Operating Lease Details (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Right-of-use lease assets	$ 339	$ 287	$ 317
Current operating lease liability	69	53	53
Non-current operating lease liability	320	281	315
Total operating lease liability	$ 389	$ 334	$ 368