You should not need any documentation about the plan itself as it will be reflected in box 10 of your W2 at the end of the year. You do want to keep track of your dependent care expenses (who you paid, $$ amounts, SSN - social security number or EIN - employer identification number of who you paid) as you will need to enter them into TurboTax when preparing next years return. For some clarification https://ttlc.intuit.com/replies/5361225
