Reserves for Future Policy Benefits and Contract Owner Account Balances (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Future policy benefits:
Total future policy benefits	$ 15,691.2	$ 14,098.4
Contract owner account balances:
Total contract owner account balance	69,319.5	69,908.3
Individual and group life insurance contracts
Future policy benefits:
Total future policy benefits	8,421.5	8,253.9
Guaranteed benefits on annuity contracts, and payout contracts with life contingencies
Future policy benefits:
Total future policy benefits	6,336.2	4,931.7
Accident and health
Future policy benefits:
Total future policy benefits	933.5	912.8
GICs
Contract owner account balances:
Total contract owner account balance	1,512.6	2,581.9
Universal life-type contracts
Contract owner account balances:
Total contract owner account balance	17,032.9	16,851.5
Fixed annuities and payout contracts without life contingencies
Contract owner account balances:
Total contract owner account balance	37,201.8	37,563.5
Fixed-indexed annuities
Contract owner account balances:
Total contract owner account balance	$ 13,572.2	$ 12,911.4