Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fixed maturities, available-for-sale	$ 60,447.2	$ 59,388.4
Equity securities	1,885.8	1,866.6
Real estate	1,699.7	1,736.7
Other investments	3,608.3	3,586.2
Other investments measured at fair value under fair value option	24.1	61.0
Separate account assets	161,302.9	159,272.7
Contractholder funds	39,813.2	38,082.5
Long-term debt	3,245.5	3,178.4
Separate account liabilities	161,302.9	159,272.7
Other liabilities	5,835.0	5,294.1
Redeemable noncontrolling interest	$ 148.5	$ 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)	476.4	474.1
Common stock, outstanding (in shares)	283.6	289.0
Treasury stock (in shares)	192.8	185.1
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale	$ 241.6	$ 268.0
Equity securities	795.5	811.4
Real estate	347.4	370.3
Other investments	208.6	139.8
Separate account assets	39,636.3	41,540.8
Contractholder funds	392.3	380.6
Long-term debt	49.1	2.8
Separate account liabilities	39,636.3	41,540.8
Other liabilities	245.9	270.2
Redeemable noncontrolling interest	$ 75.4	$ 52.4