Schedule II - Condensed Financial Information of Registrant Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Investment income from subsidiaries									$ 450.7	$ 431.8	$ 409.4
Realized Investment Gains Losses From Sales									36.6	58.2	211.6
Total revenues	$ 1,929.3	$ 1,771.0	$ 1,644.7	$ 1,868.6	$ 1,280.9	$ 1,779.7	$ 1,630.7	$ 1,330.4	7,213.7	6,021.8	6,263.1
Expenses:
Federal income taxes (credits)									265.9	67.5	164.8
Net Income (Loss)	$ 275.8	$ 202.8	$ 165.5	$ 412.2	$ (106.5)	$ 275.2	$ 197.7	$ 4.0	1,056.4	370.5	560.5
Parent Company [Member]
Revenues:
Investment income from subsidiaries									105.1	101.7	100.1
Real estate and other income									5.0	5.0	4.8
Other investment income									0.9	2.0	2.0
Realized Investment Gains Losses From Sales									(0.2)	0.0	0.0
Total revenues									110.9	108.9	107.0
Expenses:
Interest - subsidiaries									3.1	2.1	0.4
Interest - other									42.9	47.0	64.5
Real estate and other expenses									4.7	4.6	3.8
General expenses, taxes and fees									13.4	15.3	12.6
Total expenses									64.3	69.1	81.5
Revenues, net of expenses									46.6	39.7	25.4
Federal income taxes (credits)									8.8	1.5	34.1
Income (loss) before equity in earnings (losses) of subsidiaries									37.7	38.2	(8.6)
Dividends received									411.8	412.3	367.4
Earnings (losses) in excess of dividends									606.9	(80.0)	201.7
Net Income (Loss)									$ 1,056.4	$ 370.5	$ 560.5