Employee benefit plans - Plan assets by asset category segregated by level (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee benefit plans
Total assets at fair value	$ 444	$ 404	$ 352
Level 1
Employee benefit plans
Total assets at fair value	3	5
Level 3
Employee benefit plans
Total assets at fair value		1
Cash and cash equivalents
Employee benefit plans
Total assets at fair value	3	5
Cash and cash equivalents | Level 1
Employee benefit plans
Total assets at fair value	3	5
International equity securities
Employee benefit plans
Total assets at fair value		1
International equity securities | Level 3
Employee benefit plans
Total assets at fair value		1
Other
Employee benefit plans
Total assets at fair value	$ 441	$ 398