Commitments and Contingencies - Location and Amounts of Leases (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Assets
Right of use assets	$ 494	$ 676
Liabilities
Other current liabilities	100	112
Lease liabilities – non-current	$ 544	$ 620
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesCurrent	us-gaap:OtherLiabilitiesCurrent