Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 28, 2019
Basic and diluted:
Net loss attributable to common shareholders	$ (91)	$ (132)	$ (90)	$ (233)	$ (96)	$ (133)	$ (133)	$ (137)	$ (545)	$ (500)	$ (276)
Anti-dilutive shares excluded from loss per shares (in shares)									817,733	287,326	446,821
Debt conversion converted instrument, potential maximum, number of shares issued (in shares)	9,277,305								9,277,305
Convertible Debt Securities
Basic and diluted:
Anti-dilutive shares excluded from loss per shares (in shares)									9,277,305	5,515,548	0
4% Convertible Senior Notes Due 2024 | Convertible Notes Payable
Basic and diluted:
Debt instrument, conversion price (in dollars per share)	$ 22.3125								$ 22.3125			$ 22.3125