Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Fixed maturities, available-for-sale	$ 56,989.1	$ 54,846.1
Fixed maturities, trading	278.0	398.4
Equity securities, trading	1,506.3	1,413.4
Real estate	1,433.3	1,368.8
Other investments	3,283.6	3,655.9
Other investments measured at fair value under fair value option	87.4	86.2
Separate account assets	146,374.7	139,832.6
Contractholder funds	38,074.1	37,953.6
Separate account liabilities	146,374.7	139,832.6
Other liabilities	5,405.2	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)	471.9	469.2
Common stock, outstanding (in shares)	288.1	287.7
Treasury stock (in shares)	183.8	181.5
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	$ 242.3	$ 232.5
Fixed maturities, trading	0.0	82.4
Equity securities, trading	752.8	721.9
Real estate	314.4	305.7
Other investments	142.0	89.8
Separate account assets	37,956.8	35,844.1
Contractholder funds	363.9	358.7
Separate account liabilities	37,956.8	35,844.1
Other liabilities	261.5	284.1
Other liabilities measured at fair value under fair value option	0.0	59.9
Redeemable noncontrolling interest	$ 57.6	$ 58.8