Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fixed maturities, available-for-sale	$ 59,137.8	$ 54,846.1
Fixed maturities, trading	232.5	398.4
Equity securities, trading	1,670.9	1,413.4
Real estate	1,650.2	1,368.8
Other investments	3,561.3	3,655.9
Other investments measured at fair value under fair value option	88.9	86.2
Separate account assets	154,085.9	139,832.6
Contractholder funds	38,208.6	37,953.6
Separate account liabilities	154,085.9	139,832.6
Other liabilities	5,584.3	5,783.3
Redeemable noncontrolling interest	$ 129.1	$ 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)	473.5	469.2
Common stock, outstanding (in shares)	288.5	287.7
Treasury stock (in shares)	185.0	181.5
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	$ 257.4	$ 232.5
Fixed maturities, trading	0.0	82.4
Equity securities, trading	788.3	721.9
Real estate	291.9	305.7
Other investments	105.5	89.8
Separate account assets	39,725.2	35,844.1
Contractholder funds	374.5	358.7
Separate account liabilities	39,725.2	35,844.1
Other liabilities	259.2	284.1
Other liabilities measured at fair value under fair value option	0.0	59.9
Redeemable noncontrolling interest	$ 50.1	$ 58.8