Earnings per common share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net income (loss) per common share
Income from continuing operations	$ (46)	$ 83	$ (873)
Income from discontinued operations, net of tax	349	26	(377)
Net income (loss)	$ 303	$ 109	$ (1,250)
Weighted average number of common shares outstanding - basic (in shares)	60.7	59.6	58.1
Weighted dilutive effect of equity awards (in shares)		0.6
Weighted average number of common shares outstanding-diluted	60.7	60.2	58.1
Basic net income per common share:
Income from continuing operations (in dollars per share)	$ (0.76)	$ 1.39	$ (15.03)
Income from discontinued operations, net of tax (in dollars per share)	5.75	0.44	(6.49)
Basic net income (loss) per common share (in dollars per share)	4.99	1.83	(21.52)
Diluted net income per common share:
Loss from continuing operations (in dollars per share)	(0.76)	1.38	(15.03)
Income from discontinued operations, net of tax (in dollars per share)	5.75	0.43	(6.49)
Diluted net income (loss) per common share (in dollars per share)	$ 4.99	$ 1.81	$ (21.52)