Consolidated Statements of Financial Position (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fixed maturities, available-for-sale	$ 49,670.8	$ 48,757.1
Fixed maturities, trading	604.6	563.1
Equity securities, trading	840.2	716.9
Real estate	1,344.6	1,271.6
Other investments	3,209.8	2,944.4
Other investments measured at fair value under fair value option	127.2	142.9
Separate account assets	140,072.8	130,018.4
Long-term debt	2,531.2	2,601.4
Separate account liabilities	140,072.8	130,018.4
Other liabilities	5,542.2	5,224.2
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	2,500.0	2,500.0
Common stock, issued (in shares)	462.7	459.3
Common stock, outstanding (in shares)	293.9	295.2
Treasury stock (in shares)	168.8	164.1
Series A
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 100	$ 100
Preferred stock, authorized (in shares)	3.0	3.0
Preferred stock, issued (in shares)	3.0	3.0
Preferred stock, outstanding (in shares)	3.0	3.0
Series B
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, liquidation preference (in dollars per share)	$ 25	$ 25
Preferred stock, authorized (in shares)	10.0	10.0
Preferred stock, issued (in shares)	10.0	10.0
Preferred stock, outstanding (in shares)	10.0	10.0
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	278.2	272.0
Fixed maturities, trading	100.4	110.4
Equity securities, trading	345.3	327.2
Real estate	284.9	266.3
Other investments	40.6	68.1
Separate account assets	34,655.4	32,824.7
Long-term debt	82.3	47.7
Separate account liabilities	34,655.4	32,824.7
Other liabilities	344.0	362.4
Other liabilities measured at fair value under fair value option	$ 71.0	$ 104.9