The highlight of the quarter was the outperformance of the company's Optum unit, which does everything from managing prescription drug benefits to providing urgent care.

Its operating earnings gained 18 percent in the fourth quarter and accounted for the majority of the company's overall operating profit. The only other time that happened was in the fourth quarter of 2015, when the insurance business took a large charge in anticipation of Obamacare-related losses.

Related: Trump: 5 things employers are wondering about

Optum may not give up that position. UnitedHealth is doubling down on the business with its $3.2 billion purchase of Surgical Care Affiliates, which could bolster the unit's margins and revenue and will give it a presence in the growing outpatient surgery market. Other large insurers derive a greater portion of their revenue and profit from insurance alone. Optum's diversification and growth prospects are even more valuable in the face of potential Trump-related disruption to the industry.

While other big insurers were relatively slow to pull back from the ACA's individual insurance exchanges as their losses mounted, UnitedHealth started taking steps to limit its losses in late 2015 and announced a near-total exit in April 2016. That's paying dividends.

The company does not expect to lose money on the exchanges in 2017 after suffering large losses last year. Its withdrawal is helping push down its medical loss ratio, an important metric that tracks the percentage of premiums an insurance company spends on health care. A higher ratio means lower profits.

The company's quick decision-making should both boost performance this year and help limit exposure to the ultimate fate of the ACA.

The overall focus of the company's insurance operation should also be stabilizing. Optum may be the star, but the insurance business posted a 13 percent gain in both revenue and operating profit in 2016.

UnitedHealth has concentrated on increasing its share of enrollment in privately administered Medicare plans, adding 625,000 members in 2016 without any acquisitions.

Some combination of the GOP's traditional fondness for privatization and Trump's pledge to mostly leave Medicare alone should help that effort continue to pay off. The company is also the country's biggest provider of insurance to employers, which should also be relatively safe in the event of an ACA repeal.

Medicaid may see greater disruption given that it was expanded under the ACA. The fact that it's a smaller piece of the pie for UnitedHealth may come as something of a relief.

It's tough to plan for something as unpredictable as a Trump presidency. But whether it's by intent, luck, or a bit of both, UnitedHealth appears set to weather it better than most.

This column does not necessarily reflect the opinion of Bloomberg LP and its owners.

Copyright 2018 Bloomberg. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.