I work for a very large company. (Fortune 100) We also do not need to provide receipts for airline travel, nor do we need receipts for any expense below $100, provided the expenses are charged to our corporate credit cards. Any cash expense over $20 requires a receipt, and all hotel stays require receipts. It makes expense reporting quite easy.

Once every few years, a couple of my expense reports are audited to ensure compliance with corporate standards. There are also certain expenses that will flag an automatic audit and/or higher level approval, including any airfare over $500 o/w or $800 r/t. None of my expenses have ever been questioned, although I respect the trust and always follow our purchasing guidelines.

While I don't know the accounting end, so I don't know how they would substantiate the expenses, somehow they do.