A new study of 100 large companies–employing 52 million people–counts the costs. From the summary:
The cost of the ACA to large U.S. employers (10,000 or more employees) is estimated to be between $4,800 to $5,900 per employee.
These large employers will see overall ACA- related cost hikes of between $163 million and $200 million per employer, or an increase of 4.3 percent in 2016 and 8.4 percent in 2023 over and above what they would otherwise be spending. (See Appendix One for cost estimates for specific ACA provisions)
The total cost of the ACA to all large U.S. employers over the next ten years is estimated to be from $151 billion to $186 billion.