Employee benefit plans - Plan assets by asset category segregated by level (Details) - Pension - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Employee benefit plans
Total assets at fair value	$ 404	$ 352	$ 391
Level 1
Employee benefit plans
Total assets at fair value	5	2
Level 3
Employee benefit plans
Total assets at fair value	1	1
Cash and cash equivalents
Employee benefit plans
Total assets at fair value	5	2
Cash and cash equivalents | Level 1
Employee benefit plans
Total assets at fair value	5	2
International equity securities
Employee benefit plans
Total assets at fair value	1	1
International equity securities | Level 3
Employee benefit plans
Total assets at fair value	1	1
Other
Employee benefit plans
Total assets at fair value	$ 398	$ 349