回複：請教美國老土: 還是想弄清楚有關OFFER 的事

It's very typical for large companies to conduct background check. If all you have presented are true, no need to worry. It may one or two weeks, if you have international education / working background. One company I worked for even hired a local Chinese Agency to check all my education / working experience in China.

It should be a very solid offer. Congratulations!