Reconciliation of Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Insurance [Abstract]
Policy and Contract Benefits	$ 1,507.9	$ 1,484.6	$ 1,529.3
Reserves for Future Policy and Contract Benefits	44,245.9	43,540.6	45,929.4
Total Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits	45,753.8	45,025.2	47,458.7
Life Reserves for Future Policy and Contract Benefits	8,078.2	7,946.3	7,850.9
Accident and Health Active Life Reserves	10,172.9	9,704.4	9,263.5
Adjustment Related to Unrealized Investment Gains and Losses	4,253.2	3,578.4	6,150.3
Liability for Claims and Claims Adjustment Expense	$ 23,249.5	$ 23,796.1	$ 24,194.0	$ 24,535.6