Carrying Values and Estimated Fair Values of Consolidated Financial Instruments (Detail) (USD $)	Sep. 30, 2012		Dec. 31, 2011
Liabilities
Senior Notes	$ 1,815,660,000		$ 299,035,000
Carrying Value
Assets
Investments (excluding equity method investments)	18,116,000,000	[1]	4,670,600,000	[1]
Liabilities
Senior Notes	1,815,700,000	[2]	299,000,000	[2]
Fair Value
Assets
Investments (excluding equity method investments)	18,116,000,000	[1]	4,670,600,000	[1]
Liabilities
Senior Notes	$ 1,974,200,000	[2]	$ 314,800,000	[2]

[1] This table includes AFS investments (debt and equity securities as well as partnership investments carried at fair value that are included in other invested assets). This table excludes investments accounted for using the equity method (including Homesite, ORX and other equity method investments) and certain loans receivable that are carried at cost, all of which are included in other invested assets. The fair value of short-term investments approximates amortized cost. The fair value of all other categories of investments is discussed below.

[2] See Note 8 for additional information on the Senior Notes.