Buried in October's financial bailout package was a landmark provision, 12 years in the making, that for the first time requires insurance companies to provide equal coverage for mental and physical health. Bipartisan advocates say the new law could improve care — and reduce stigma — for the 80 million Americans suffering from mental illness and substance abuse. Many insurers largely favor the requirement, in part because research suggests a strong link between conditions such as untreated depression and physical ailments.