Calculation of Total Purchase Price for Old Transatlantic as of Acquisition Date (Parenthetical) (Detail) (TransRe, USD $) In Millions, except Per Share data, unless otherwise specified	0 Months Ended
	Mar. 06, 2012
TransRe
Business Acquisition [Line Items]
Portion of purchase price based on cash consideration	$ 816.0
Shares on Transatlantic common stock outstanding	57.4
Per share value of consideration paid for Transatlantic common stock	$ 14.22
Transatlantic shares not included in the determination of cash consideration	0.2	[1]

[1] The $816.0 million cash consideration was fixed as of the date of the Merger Agreement, predicated on the 57.4 million shares of common stock of Old TransRe outstanding at that date multiplied by $14.22 per share. Therefore, the additional 0.2 million of Old TransRe shares outstanding as of the TransRe Acquisition Date do not cause the cash consideration to increase and are adjusted for in this presentation.