Income Taxes - Valuation Allowances Against Deferred Tax Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Valuation Allowances Against Deferred Tax Assets
Held for sale	$ 0	$ (47)
Deferred tax asset valuation allowance
Valuation Allowances Against Deferred Tax Assets
Allowances at beginning of year	179	125
Allowances at end of year	323	179
Deferred tax asset valuation allowance | Benefits reserved current year
Valuation Allowances Against Deferred Tax Assets
Benefits reserved current year	133	102
Deferred tax asset valuation allowance | Translation difference
Valuation Allowances Against Deferred Tax Assets
Translation difference	$ 11	$ (1)