Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Fixed maturities, available-for-sale	$ 60,108.5	$ 59,388.4
Equity securities	1,843.7	1,866.6
Real estate	1,729.7	1,736.7
Other investments	4,310.3	3,586.2
Other investments measured at fair value under fair value option	23.6	61.0
Separate account assets	144,987.9	159,272.7
Contractholder funds	39,699.7	38,082.5
Long-term debt	3,259.6	3,178.4
Separate account liabilities	144,987.9	159,272.7
Other liabilities	5,661.9	5,294.1
Redeemable noncontrolling interest	$ 391.2	$ 101.3
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)	476.7	474.1
Common stock, outstanding (in shares)	279.5	289.0
Treasury stock (in shares)	197.2	185.1
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	$ 94.5	$ 268.0
Equity securities	774.8	811.4
Real estate	364.0	370.3
Other investments	457.9	139.8
Separate account assets	37,183.3	41,540.8
Contractholder funds	396.0	380.6
Long-term debt	58.4	2.8
Separate account liabilities	37,183.3	41,540.8
Other liabilities	104.9	270.2
Redeemable noncontrolling interest	$ 325.7	$ 52.4