Statutory Financial Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Traditional U.S. Life Insurance Subsidiaries
Statutory Accounting Practices
Statutory Net Income	$ 855.1	$ 653.7	$ 628.9
Statutory Combined Net Gain (Loss) from Operations	884.6	689.2	623.9
Statutory Combined Capital and Surplus	3,626.9	3,470.3
Captive Reinsurers
Statutory Accounting Practices
Statutory Net Income	48.4	(56.3)	(129.3)
Statutory Combined Net Gain (Loss) from Operations	50.6	(54.3)	$ (130.2)
Statutory Combined Capital and Surplus	$ 1,726.7	$ 1,672.3