Income Taxes - Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Operating Loss Carryforwards [Line Items]
Interest limitation carry forwards	$ 22	$ 157
R&D and state credit carry forwards	42	$ 40
Federal
Operating Loss Carryforwards [Line Items]
NOL carry forwards	1,609
Interest limitation carry forwards	78
R&D and state credit carry forwards	44
State
Operating Loss Carryforwards [Line Items]
NOL carry forwards	1,488
Interest limitation carry forwards	118
R&D and state credit carry forwards	0
Foreign
Operating Loss Carryforwards [Line Items]
NOL carry forwards	274
Interest limitation carry forwards	14
R&D and state credit carry forwards	$ 0