Carrying Values and Estimated Fair Values of Consolidated Financial Instruments (Detail) - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Assets
Investments (excluding equity method investments)		$ 17,935.9	$ 18,153.8
Liabilities
Senior Notes		1,888.5	1,948.6
Carrying Value
Assets
Investments (excluding equity method investments)	[1]	17,935.9	18,153.8
Liabilities
Senior Notes	[2]	1,759.5	1,767.1
Fair Value
Assets
Investments (excluding equity method investments)	[1]	17,935.9	18,153.8
Liabilities
Senior Notes	[2]	$ 1,888.5	$ 1,948.6

[1] This table includes available-for-sale ("AFS") investments (debt and equity securities as well as partnership and non-marketable equity investments carried at fair value that are included in other invested assets). This table excludes investments accounted for using the equity method 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. Fair value for all other categories of investments is discussed in Note 1(c) to Notes to Consolidated Financial Statements set forth in Part II, Item 8, "Financial Statements and Supplementary Data" of the 2014 10-K

[2] See Note 8 to Notes to Consolidated Financial Statements set forth in Part II, Item 8, "Financial Statements and Supplementary Data" of the 2014 10-K.