Liability for Unpaid Claims and Claims Adjustment Expenses Reconciliation of Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Insurance [Abstract]
Policy and Contract Benefits	$ 1,720.5	$ 1,695.7	$ 1,674.1
Reserves for Future Policy and Contract Benefits	48,060.8	44,841.9	45,092.7
Total Policy and Contract Benefits and Reserves for Future Policy and Contract Benefits	49,781.3		46,766.8
Life Reserves for Future Policy and Contract Benefits	8,396.2		8,303.4
Accident and Health Active Life Reserves	12,092.9		11,521.5
Adjustment Related to Unrealized Investment Gains and Losses	6,334.2		3,684.9
Liability for Unpaid Claims and Claim Adjustment Expenses	$ 22,958.0	$ 23,149.0	$ 23,257.0	$ 23,222.0