Significant Accounting Policies (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Policy Loans		$ 3,051.4	$ 2,996.1
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment		670.9	641.6
Present Value of Future Insurance Profits		30.3	37.6
Accumulated Amortization of Other Deferred Costs		119.3	112.5
Present Value of Future Insurance Profits, Amortization Expense		7.4	7.4	7.8
Deferred Revenue and Credits		81.0	100.2
Premium tax expense		134.9	129.4	130.2
Assets, Participation Fund Account (PFA)		385.5	364.4
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	407.0		459.0	455.0
Policy Loans Ceded
Policy Loans		$ 2,838.3	$ 2,790.5