The contract is reportedly for four years and $72 million and should surpass the $48.5 million guaranteed contract given to Tom Brady by the New England Patriots. [EDIT:] As has been pointed out in the comments, AHN misquoted a USA Today article. This should have read: Colts offer Manning a deal greater than the four-year, $72 million deal given to Brady. No word yet on how large the contract is or how much of the contract is expected to be guaranteed, but all signs point to everything in Manning's deal eclipsing Brady's deal.
It's also worth noting that Irsay plans to offer Manning a five or six-year deal.
We'll stay tuned, obviously, and will hopefully see a contract hammered out sometime before the current CBA expires (in other words, in the next few weeks.