Employee benefit plans - Target Asset Allocations (Details)	Dec. 31, 2020
Target asset allocations for each major category of the plan assets
Target	100.00%
Actual	100.00%
Percentage points to rebalance the portfolio within	2.00%
Cash and cash equivalents
Target asset allocations for each major category of the plan assets
Target	1.00%
Actual	1.00%
U.S. equity securities
Target asset allocations for each major category of the plan assets
Target	71.00%
Actual	71.00%
Fixed income
Target asset allocations for each major category of the plan assets
Target	28.00%
Actual	28.00%