Variable Interest Entities (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Carrying amounts of consolidated VIE assets and liabilities
Fixed maturities, available-for-sale	$ 49,627.5	$ 48,757.1
Fixed maturities, trading	609.4	563.1
Equity securities, trading	807.6	716.9
Real estate	1,352.1	1,271.6
Other investments	2,990.9	2,944.4
Accrued investment income	545.1	532.1
Separate account assets	138,296.7	130,018.4
Other assets	1,054.7	1,134.2
Total assets	216,422.8	208,191.4
Long-term debt	2,529.2	2,601.4
Deferred income taxes	1,150.6	824.0
Separate account liabilities	138,296.7	130,018.4
Other liabilities	4,984.6	5,224.2
Total liabilities	205,997.7	198,167.2
Aggregate consolidated variable interest entities
Carrying amounts of consolidated VIE assets and liabilities
Fixed maturities, available-for-sale	287.2	272.0
Fixed maturities, trading	100.4	110.4
Equity securities, trading	349.4	327.2
Real estate	276.2	266.3
Other investments	46.2	68.1
Cash	6.2	12.0
Accrued investment income	2.1	2.0
Separate account assets	35,079.9	32,824.7
Other assets	0.2	0.1
Total assets	36,147.8	33,882.8
Long-term debt	74.9	47.7
Deferred income taxes	1.6	1.5
Separate account liabilities	35,079.9	32,824.7
Other liabilities	349.5	362.4
Total liabilities	35,505.9	33,236.3
Grantor trusts
Consolidated Variable Interest Entity disclosures
Number of consolidated variable interest entities	3
Carrying amounts of consolidated VIE assets and liabilities
Fixed maturities, available-for-sale	287.2	272.0
Accrued investment income	0.4	0.3
Total assets	287.6	272.3
Deferred income taxes	1.6	1.5
Other liabilities	242.0	217.2
Total liabilities	243.6	218.7
Collateralized private investment vehicle
Consolidated Variable Interest Entity disclosures
Number of entities for which the reporting entity acts as primary beneficiary	1
Carrying amounts of consolidated VIE assets and liabilities
Fixed maturities, trading	100.4	110.4
Total assets	100.4	110.4
Other liabilities	86.9	93.8
Total liabilities	86.9	93.8
Commercial mortgage-backed securities VIE
Carrying amounts of consolidated VIE assets and liabilities
Other investments	41.9	68.1
Accrued investment income	0.2	0.6
Total assets	42.1	68.7
Other liabilities	4.9	31.4
Total liabilities	4.9	31.4
Mandatory retirement savings
Carrying amounts of consolidated VIE assets and liabilities
Equity securities, trading	349.4	327.2
Separate account assets	35,079.9	32,824.7
Total assets	35,429.3	33,151.9
Separate account liabilities	35,079.9	32,824.7
Total liabilities	35,079.9	32,824.7
Real estate VIE
Carrying amounts of consolidated VIE assets and liabilities
Real estate	276.2	266.3
Other investments	4.3
Cash	6.2	12.0
Accrued investment income	1.5	1.1
Other assets	0.2	0.1
Total assets	288.4	279.5
Long-term debt	74.9	47.7
Other liabilities	15.7	20.0
Total liabilities	$ 90.6	$ 67.7