(Reuters) - After weeks of discussions behind closed doors, the U.S. Senate unveiled a draft of its healthcare bill on Thursday that would overhaul the Affordable Care Act, commonly known as Obamacare.  The House of Representatives narrowly passed its healthcare bill last month. If the Senate passes its bill, the House will either have to vote on the Senate version of the legislation or the two chambers will have to reconcile their differences in a conference committee.  Obamacare extended coverage to some 20 million additional Americans through both subsidized private insurance and an expansion of Medicaid. Since its passage in 2010, Republicans have campaigned on repealing the program and argued that the law is too costly and represents undue government interference in Americans’ healthcare.  Here is how the two bills compare on their main provisions:  Under Obamacare, more than 30 states, including about a dozen states with Republican governors, expanded the Medicaid government health insurance program for the poor and disabled. Both bills would roll back the expansion and significantly overhaul the program, which provides insurance to nearly 70 million people. SENATE: The draft legislation would phase out Obamacare’s expansion of Medicaid over three years, from 2021 to 2024. It would then overhaul the program and reduce its federal funding more than the House bill would, beginning in 2025. HOUSE: The bill would allow the Medicaid expansion to continue until Jan. 1, 2020. After that date, expansion would end, and people who enrolled in the expansion could not re-enroll once they leave. Medicaid funding would be capped on a per-person basis. SENATE: The bill would repeal most Obamacare taxes beginning after Dec. 31, 2016, including the 3.8 percent net investment income tax on wealthy Americans. The tax on branded prescription brands would be repealed in 2018, and the legislation would delay the so-called Cadillac tax on high-cost employer-provided insurance. It would also provide more generous tax credits for the purchase of private health insurance for people between zero and 350 percent of the federal poverty level based on income. Under Obamacare, those between 100 and 400 percent of the federal poverty level were eligible for tax credits.  HOUSE: The bill would repeal most Obamacare taxes retroactively after Dec. 31, 2016, and delay the Cadillac tax to 2026. It would provide flat age-based tax credits for the purchase of private health insurance ranging from $2,000 to $4,000 per year that would be capped at upper-income levels.  Both bills would repeal the penalties associated with the individual mandate that nearly everyone purchase health insurance or else pay a fine, and the mandate that employers provide insurance to employees.  SENATE: The legislation would maintain the popular Obamacare provision that young adults be allowed to stay on their parents’ health insurance until age 26. It would also prevent insurers from discriminating against those with pre-existing conditions, but would give states flexibility to opt out of so-called essential health benefits, such as maternity care and prescription drug coverage, that experts said could make it harder for some sick people to find affordable plans. The bill would also allow insurers to charge older Americans up to five times more than younger Americans. HOUSE: The bill would allow young adults to remain on their parents’ insurance until age 26. It would allow states to opt out of essential health benefits and Obamacare’s requirement that insurers charge sick and healthy people the same rates. It would also let insurers mark up premiums by 30 percent for those who have a lapse in insurance coverage of about two months or more. Insurers could charge older Americans up to five times more than younger Americans. 