OP wasn't the one who necessarily wanted the additional insurance but this is an excerpt from USA Today:
"American Express also offers a premium car rental insurance program for a fee. Coverage through the premium insurance is primary, so you won’t have to file with your other insurance company before making a claim. The coverage amount is increased to $100,000 for loss or damage, and additional coverage is provided for medical expenses or accidental death. The length of coverage also is extended to 42 consecutive days."
http://traveltips.usatoday.com/american-express-card-car-rental-insurance-policy-1649.html
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