Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fixed maturities, available-for-sale	$ 49,966.5	$ 49,670.8
Fixed maturities, trading	686.8	604.6
Equity securities, available-for-sale	104.5	123.0
Equity securities, trading	1,202.7	840.2
Real estate	1,451.8	1,344.6
Other investments	3,251.7	3,209.8
Other investments measured at fair value under fair value option	53.4	127.2
Separate account assets	136,978.9	140,072.8
Contractholder funds	35,716.1	34,726.7
Long-term debt	3,290.8	2,531.2
Separate account liabilities	136,978.9	140,072.8
Other liabilities	$ 5,678.4	$ 5,542.2
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)	466.2	462.7
Common stock, outstanding (in shares)	291.4	293.9
Treasury stock (in shares)	174.8	168.8
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)	0.0	3.0
Preferred stock, issued (in shares)	0.0	3.0
Preferred stock, outstanding (in shares)	0.0	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)	0.0	10.0
Preferred stock, issued (in shares)	0.0	10.0
Preferred stock, outstanding (in shares)	0.0	10.0
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	$ 257.4	$ 278.2
Fixed maturities, trading	100.4	100.4
Equity securities, trading	640.9	345.3
Real estate	354.5	284.9
Other investments	29.5	40.6
Separate account assets	33,300.4	34,655.4
Contractholder funds	338.9
Long-term debt	42.8	82.3
Separate account liabilities	33,300.4	34,655.4
Other liabilities	345.9	344.0
Other liabilities measured at fair value under fair value option	$ 68.1	$ 71.0