Reconciliation of Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Reconciliation of Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Policy and Contract Benefits	$ 1,494.0	$ 1,565.0	$ 1,736.9
Reserves for Future Policy and Contract Benefits	43,051.9	39,715.0	37,740.8
Total	44,545.9	41,280.0	39,477.7
Life Reserves for Future Policy and Contract Benefits	7,454.2	7,380.7	7,247.5
Accident and Health Active Life Reserves	7,259.6	6,451.6	5,999.8
Unrealized Adjustment to Reserves for Future Policy and Contract Benefits	5,245.6	3,108.3	1,644.7
Liability for Claims and Claims Adjustment Expense	$ 24,586.5	$ 24,339.4	$ 24,585.7	$ 24,419.0