Consolidated Statements of Financial Position (Parenthetical) - USD ($) shares in Millions, $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fixed maturities, available-for-sale	$ 78,710.3	$ 70,106.2
Equity securities	2,013.4	1,879.4
Mortgage loans	17,343.0	16,486.9
Real estate	1,797.3	1,714.8
Other investments	5,126.8	4,690.2
Other investments measured at fair value under fair value option	28.5	22.8
Separate account assets	175,951.4	165,468.0
Contractholder funds	43,237.7	41,367.5
Long-term debt	4,279.2	3,734.1
Separate account liabilities	175,951.4	165,468.0
Other liabilities	7,582.1	6,863.7
Redeemable noncontrolling interest	$ 255.6	$ 264.9
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)	481.9	479.3
Common stock, outstanding (in shares)	273.3	276.6
Treasury stock (in shares)	208.6	202.7
Aggregate consolidated variable interest entities
Fixed maturities, available-for-sale		$ 99.4
Equity securities	$ 902.5	810.9
Mortgage loans	319.0
Real estate	476.8	457.6
Other investments	348.5	263.7
Separate account assets	41,138.9	39,130.3
Contractholder funds	388.6	394.6
Long-term debt		64.2
Separate account liabilities	41,138.9	39,130.3
Other liabilities	24.5	124.4
Redeemable noncontrolling interest	$ 226.8	$ 215.4