Income taxes - Components of deferred tax assets and liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of deferred tax assets and liabilities:
Tax benefit of losses carried forward	$ 219	$ 222	$ 198
Research and development tax credits	82	91	72
Construction contract assets and liabilities	89	77	67
Property and equipment		15	3
Trade and other payables	41	38	25
Employee benefits	41	49	53
Unrealized foreign exchange gains and losses	6	6	5
Other	18	21	8
Deferred tax assets	496	519	431
Valuation allowance	(231)	(304)	(134)
Deferred tax assets, net of valuation allowance	265	215	297
Property and equipment	(47)
Goodwill and intangibles	(124)	(213)	(301)
Outside basis difference in assets held for sale	(78)
Other	(10)	(2)
Deferred tax liabilities	(259)	$ (215)	(301)
Deferred tax assets and (liabilities), net			$ (4)
Deferred tax assets and (liabilities), net	6
Decrease in valuation allowance	73
Deferred tax liability on investments	$ 78