Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fixed maturities, available-for-sale	$ 57,799.8	$ 54,846.1
Fixed maturities, trading	241.3	398.4
Equity securities, trading	1,586.4	1,413.4
Real estate	1,441.8	1,368.8
Other investments	3,297.9	3,655.9
Other investments measured at fair value under fair value option	85.7	86.2
Separate account assets	149,347.9	139,832.6
Contractholder funds	38,199.8	37,953.6
Separate account liabilities	149,347.9	139,832.6
Other liabilities	5,360.9	5,783.3
Redeemable noncontrolling interest	$ 95.1	$ 97.5
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)	472.8	469.2
Common stock, outstanding (in shares)	288.6	287.7
Treasury stock (in shares)	184.2	181.5
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	$ 250.1	$ 232.5
Fixed maturities, trading	0.0	82.4
Equity securities, trading	763.3	721.9
Real estate	319.2	305.7
Other investments	168.1	89.8
Separate account assets	37,926.8	35,844.1
Contractholder funds	370.8	358.7
Separate account liabilities	37,926.8	35,844.1
Other liabilities	266.3	284.1
Other liabilities measured at fair value under fair value option	0.0	59.9
Redeemable noncontrolling interest	$ 49.7	$ 58.8