Carrying Values and Estimated Fair Values of Consolidated Financial Instruments (Detail) - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Assets
Investments (excluding equity method investments and loans)		$ 17,029.3	$ 17,007.6
Liabilities
Senior Notes		1,535.4	1,488.7
Carrying Value
Assets
Investments (excluding equity method investments and loans)	[1]	17,029.3	17,007.6
Liabilities
Senior Notes	[2]	1,383.6	1,383.1
Fair Value
Assets
Investments (excluding equity method investments and loans)	[1]	17,029.3	17,007.6
Liabilities
Senior Notes	[2]	$ 1,535.4	$ 1,488.7

[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 commercial mortgage loans that are carried at unpaid principal balance. The fair value of short-term investments approximates amortized cost. The fair value of 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 2015 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 2015 10-K for additional information on the senior notes.