Employee plans - Company's Investment Policy Targets and Ranges for Each Asset Category (Details) - Pension Plans	Dec. 31, 2019
U.S. Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	42.00%
U.S. Plans | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	38.00%
U.S. Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
U.S. Plans | Cash
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
U.S. Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	20.00%
U.S. Plans | Minimum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	36.00%
U.S. Plans | Minimum | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	35.00%
U.S. Plans | Minimum | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
U.S. Plans | Minimum | Cash
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
U.S. Plans | Minimum | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	10.00%
U.S. Plans | Maximum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	48.00%
U.S. Plans | Maximum | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	41.00%
U.S. Plans | Maximum | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
U.S. Plans | Maximum | Cash
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	5.00%
U.S. Plans | Maximum | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	30.00%
International Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	19.00%
International Plans | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	61.00%
International Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	1.00%
International Plans | Cash
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	1.00%
International Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	18.00%
International Plans | Minimum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	16.00%
International Plans | Minimum | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	54.00%
International Plans | Minimum | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
International Plans | Minimum | Cash
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	0.00%
International Plans | Minimum | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	11.00%
International Plans | Maximum | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	23.00%
International Plans | Maximum | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	67.00%
International Plans | Maximum | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	3.00%
International Plans | Maximum | Cash
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	5.00%
International Plans | Maximum | Other
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan target allocation percentage of assets	26.00%