Here's some of what I've managed to find out regarding the insuring of the Titanic.
The insurance company that had insured the Titanic was Lloyds of London. The ship was insured for five million dollars, even though the ship and her cargo probably cost more than ten million. This according to a newspaper account in Dave Bryceson's book "The Titanic Disaster - as Reported in the British Press".
However, there may have been something of a dispute between Lloyds and the White Star Line. In a letter to July 8, 1912 edition of The London Times, the secretary to the office of Lloyds Register of British and Foreign Shipping wrote:
"TO THE EDITOR OF THE TIMES
Sir, - In view of the reports which have appeared in the Press in connexion (sic) with the inquiry into the loss of the S. S. Titanic, to the effect that the vessel was built considerable in excess of the requirements of Lloyd's Register, I am directed to say that those statements are inaccurate. On the contrary, in important parts of her construction the vessel as built did not come up to the requirements of Lloyd's Register for a vessel of her dimensions.
I do not for a moment suggest that this circumstance had any bearing whatever on the loss of the vessel, and therefore, for obvious reasons, this letter has been delayed until after the close of the Inquiry. But, in justice to this society and to those who rely upon its classification, it is felt to be only right to dispel the erroneous impression which might be created regarding the standard of classification of Lloyd's Register for such vessels if the statements referred to remain uncontradicted.
I am, Sir, your obedient servant,
A, Scott, Secretary"
According to an article in the New York Herald just after the collision, the Hartford Underwriters estimated that the amount was over fifteen million. Also, according to "Gray Days and Gold" by John Cosgrove, privately published in 1967, "Of the $140,000 placed in the American insurance market on the majestic liner's hull, the Atlantic Mutual Company carried $100,000."