Significant Accounting Policies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) Integer	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of Operating Segments | Integer	3
Ceded Policy Loans	$ 3,150.1	$ 3,068.4
Accumulated Depreciation for Property and Equipment	902.6	823.3
Value of Business Acquired	24.0	15.2
Accumulated Amortization of Value of Business Acquired	133.1	134.7
Amortization of Value of Business Acquired	4.6	3.5	$ 4.5
Deferred Gain on Reinsurance	31.9	41.7
Premium tax expense	146.5	139.2	$ 137.0
Participation Fund Account Assets (PFA)	$ 338.8	$ 358.6