Total Fair Value of Net Assets Acquired and Gain on Bargain Purchase as of Acquisition Date (Detail) (USD $)	9 Months Ended	1 Months Ended	3 Months Ended	7 Months Ended
	Sep. 30, 2012	Mar. 06, 2012 Transatlantic	Sep. 30, 2012 Transatlantic	Sep. 30, 2012 Transatlantic	Mar. 06, 2012 Transatlantic Deferred Acquisition Costs	Mar. 06, 2012 Transatlantic Intangible Assets	Mar. 06, 2012 Transatlantic Net deferred tax assets	Mar. 06, 2012 Transatlantic All other assets	Mar. 06, 2012 Transatlantic Senior Notes
Schedule of Net Assets Acquired and Gain on Bargain Purchase [Line Items]
Net book value of net assets acquired prior to fair value adjustments		$ 4,062,700,000
Change in net assets acquired for fair value adjustment, assets					(250,700,000)	323,500,000	21,500,000	(25,300,000)
Change in net assets acquired for fair value adjustment, liabilities									(124,400,000)
Fair value of net assets acquired		4,007,300,000
Less purchase price		(3,512,400,000)
Gain on bargain purchase (before all Transaction Costs)	$ 494,940,000	$ 494,900,000