SCHEDULE II - Condensed Financial Information of Registrant (Parent Company) - Balance Sheet (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Assets:
Equity securities at fair value	$ 135.3	$ 131.1
Other assets	580.8	519.1
Total assets	33,339.2	36,204.4		$ 33,613.1
Liabilities:
Notes payable	1,138.8	1,137.3
Other liabilities	693.9	830.9
Total liabilities	31,938.4	30,944.7
Commitments and Contingencies
Shareholders' equity:
Accumulated other comprehensive income (loss)	(2,093.1)	1,947.1
Retained earnings	1,459.0	1,127.2		517.9
Total shareholders' equity	1,400.8	5,259.7	$ 5,484.2	$ 4,659.2	$ 4,677.0
Total liabilities and shareholders' equity	33,339.2	36,204.4
Parent Company
Assets:
Cash and cash equivalents - unrestricted	136.7	196.2
Equity securities at fair value	36.6	49.9
Investment in wholly-owned subsidiaries (eliminated in consolidation)	2,292.4	6,054.3
Income tax assets, net	154.9	164.5
Receivable from subsidiaries (eliminated in consolidation)	114.9	156.9
Other assets	2.2	1.2
Total assets	2,737.7	6,623.0
Liabilities:
Notes payable	1,138.8	1,137.3
Payable to subsidiaries (eliminated in consolidation)	172.0	146.9
Other liabilities	26.1	79.1
Total liabilities	1,336.9	1,363.3
Commitments and Contingencies
Shareholders' equity:
Common stock and additional paid-in capital ($0.01 par value, 8,000,000,000 shares authorized, shares issued and outstanding: 2022 - 114,343,070; 2021 - 120,377,152)	2,034.9	2,185.4
Accumulated other comprehensive income (loss)	(2,093.1)	1,947.1
Retained earnings	1,459.0	1,127.2
Total shareholders' equity	1,400.8	5,259.7
Total liabilities and shareholders' equity	$ 2,737.7	$ 6,623.0