Around here, the document you're looking for is the "Certificate of coverage". Contact your HR and see if they can get it for you. It's normally a long book with a ton of details. Sometimes you'll get it after you sign up, but if you're persistent, they can normally get it for you pre signing up.
Having said that, you might want to look and see if there is an alternative to the ER in your town. We have a place that's a hybrid between an urgent care and an ER. They do everything a simple urgent care can do and more. This is the list off their website:
What We Treat
Lacerations, sprains, fractures, minor auto accidents
Eye injuries, nosebleeds
Earaches, sore throats, coughs, fever, asthma attacks
Abdominal pain, vomiting and diarrhea, dehydration
Urinary tract infections
Rashes, bites, skin infections, allergic reactions
Back and neck pain
Minor burns
My wife was dehydrated during pregnancy, because she had the flu with morning sickness. We knew she needed an IV. We could have gone to the ER, but it would have taken 5-7 hours and cost $200 copay or $600-1500 without insurance. Instead, we went to the other place. They hooked her up to an IV. Took under two hours and cost us $20 copay or $150-200 without insurance. My wife cut her finger down to the bone a month ago. She went to the emergicare and they stitched it right up. She was home in under an hour. If you need more care, they'll transfer you to the ER. It's really a much better option if you value your time and money. Just don't cheap out when you need real care. My wife had trouble breathing...yeah, we went straight to the ER. Turns out she had a pulmonary embolism (blood clot in her lungs) that could have killed her.
...Yeah, in case you hadn't guessed, we have the platinum insurance plan because of my wife. Luckily, my premiums are crazy cheap. Hurray for state government! I still miss my $25 ER co-pay from my last job. That was epic awesome. Still, with my new insurance, the 5 day hospital stay for child birth cost us $0. The 5 day pulmonary embolism hospital stay cost us $0. Thank you tax payers.