Earnings (loss) per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Numerator for earnings (loss) per share, basic
Net income (loss) attributable to controlling interest	$ (130)	$ 359	$ (332)	$ (530)
Earnings (loss) for per share calculation	$ (130)	$ 359	$ (332)	$ (530)
Denominator for earnings (loss) per share, basic
Weighted-average shares outstanding (in shares)	651.0	615.0	629.0	614.0
Effect of share-based awards (in shares)	2.0	1.0	1.0	1.0
Weighted-average shares for per share calculation, basic (in shares)	653.0	616.0	630.0	615.0
Earnings (loss) per share, basic (in dollars per share)	$ (0.20)	$ 0.58	$ (0.53)	$ (0.86)
Numerator for earnings (loss) per share, diluted
Net income (loss) attributable to controlling interest	$ (130)	$ 359	$ (332)	$ (530)
Effect of interest expense on convertible debt instruments		1
Earnings (loss) for per share calculation	$ (130)	$ 360	$ (332)	$ (530)
Denominator for earnings (loss) per share, diluted
Weighted-average shares outstanding (in shares)	651.0	615.0	629.0	614.0
Effect of share-based awards, diluted	2.0	3.0	1.0	1.0
Effect of convertible debt instruments, diluted		84.0
Weighted-average shares for per share calculation, diluted	653.0	702.0	630.0	615.0
Earnings (loss) per share, diluted (in dollars per share)	$ (0.20)	$ 0.51	$ (0.53)	$ (0.86)
Share-based awards
Anti-dilutive securities
Securities excluded from earnings per share calculation (in shares)	13.0	7.9	12.3	10.8
Convertible debt
Anti-dilutive securities
Securities excluded from earnings per share calculation (in shares)	108.1		103.1	84.0
0.50% Exchangeable Senior Bonds due January 2023
Anti-dilutive securities
Debt instrument interest rate stated percentage	0.50%	0.50%	0.50%	0.50%
2.50% Senior Guaranteed Exchangeable Bonds due January 2027
Anti-dilutive securities
Debt instrument interest rate stated percentage	2.50%	2.50%	2.50%	2.50%
4.00% Senior Guaranteed Exchangeable Bonds due December 2025
Anti-dilutive securities
Debt instrument interest rate stated percentage	4.00%		4.00%