Earnings per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Earnings per share
Income (loss) from continuing operations	$ 53	$ (41)	$ 139	$ (68)	$ (485)	$ (309)	$ (52)	$ (27)	$ 83	$ (873)	$ (56)
Net (income) loss from discontinued operations	(10)	16	9	11	(456)	23	15	41	26	(377)	116
Net income (loss)	$ 43	$ (25)	$ 148	$ (57)	$ (941)	$ (286)	$ (37)	$ 14	$ 109	$ (1,250)	$ 60
Weighted average number of common shares outstanding - basic (in shares)									59.6	58.1	41.2
Weighted dilutive effect of equity awards (in shares)									0.6
Weighted average number of common shares outstanding-diluted									60.2	58.1	41.2
Basic income (loss) per common share:
Basic Income (loss) from continuing operations (in dollars per share)	$ 0.89	$ (0.69)	$ 2.33	$ (1.14)	$ (8.18)	$ (5.22)	$ (0.91)	$ (0.48)	$ 1.39	$ (15.03)	$ (1.36)
Basic income (loss) from discontinued operations, net of tax (in dollars per share)	(0.17)	0.27	0.15	0.18	(7.69)	0.39	0.26	0.73	0.44	(6.49)	2.82
Basic income (loss) per common share (in dollars per share)	0.72	(0.42)	2.48	(0.96)	(15.87)	(4.83)	(0.65)	0.25	1.83	(21.52)	1.46
Diluted income (loss) per common share:
Diluted Income (loss) from continuing operations (in dollars per share)	0.87	(0.69)	2.32	(1.14)	(8.18)	(5.22)	(0.91)	(0.48)	1.38	(15.03)	(1.36)
Diluted income (loss)from discontinued operations, net of tax (in dollars per share)	(0.17)	0.27	0.15	0.18	(7.69)	0.39	0.26	0.73	0.43	(6.49)	2.82
Diluted income (loss) per common share (in dollars per share)	$ 0.70	$ (0.42)	$ 2.47	$ (0.96)	$ (15.87)	$ (4.83)	$ (0.65)	$ 0.25	$ 1.81	$ (21.52)	$ 1.46