Segment Information - Financial Information by Segment (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) segment	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Revenues
Net earned premiums	$ 2,150.6	$ 2,021.3	$ 4,256.2	$ 4,086.8
Fees and other income	298.5	236.4	548.4	620.0
Net investment income	82.9	65.4	159.2	149.0
Net realized gains on investments	10.3	28.9	11.1	(55.1)
Total revenues	2,542.3	2,352.0	4,974.9	4,800.7
Benefits, losses and expenses
Policyholder benefits	538.3	523.6	1,067.0	1,058.8
Amortization of deferred acquisition costs and value of business acquired	991.4	867.0	1,938.1	1,762.3
Underwriting, general and administrative expenses	747.2	725.4	1,482.9	1,618.0
Interest expense	28.8	26.7	57.2	52.2
Total benefits, losses and expenses	2,305.7	2,142.7	4,545.2	4,491.3
Segment income (loss) from continuing operations before provision (benefit) for income taxes	236.6	209.3	429.7	309.4
Provision (benefit) for income taxes	51.9	44.6	96.5	(3.9)
Net income from continuing operations	184.7	164.7	333.2	313.3
Net income from discontinued operations (Note 4)	18.9	13.7	33.2	20.9
Net income	203.6	178.4	366.4	334.2
Less: Net income attributable to non-controlling interests	(0.2)	(0.3)	0.0	(1.4)
Net income attributable to stockholders	203.4	178.1	366.4	332.8
Less: Preferred stock dividends	0.0	(4.6)	(4.7)	(9.3)
Net income attributable to common stockholders	203.4	173.5	361.7	323.5
Net income attributable to common stockholders	203.4	173.5	361.7	323.5
Segment assets	45,994.8		45,994.8		$ 44,649.9
Global Lifestyle
Revenues
Net earned premiums	1,677.4	1,568.1	3,326.1	3,165.8
Fees and other income	260.4	200.6	474.0	549.8
Net investment income	49.4	44.2	100.2	98.9
Net realized gains on investments	0.0	0.0	0.0	0.0
Total revenues	1,987.2	1,812.9	3,900.3	3,814.5
Benefits, losses and expenses
Policyholder benefits	344.8	343.1	672.2	679.3
Amortization of deferred acquisition costs and value of business acquired	932.6	810.8	1,821.8	1,649.2
Underwriting, general and administrative expenses	548.2	500.7	1,075.4	1,168.6
Interest expense	0.0	0.0	0.0	0.0
Total benefits, losses and expenses	1,825.6	1,654.6	3,569.4	3,497.1
Segment income (loss) from continuing operations before provision (benefit) for income taxes	161.6	158.3	330.9	317.4
Provision (benefit) for income taxes	37.8	36.5	78.0	74.7
Net income from continuing operations	123.8	121.8	252.9	242.7
Segment assets	25,183.3		25,183.3
Global Housing
Revenues
Net earned premiums	473.2	453.2	930.1	921.0
Fees and other income	37.9	35.7	74.0	68.3
Net investment income	23.7	16.4	43.1	38.4
Net realized gains on investments	0.0	0.0	0.0	0.0
Total revenues	534.8	505.3	1,047.2	1,027.7
Benefits, losses and expenses
Policyholder benefits	193.5	180.4	394.8	379.1
Amortization of deferred acquisition costs and value of business acquired	58.8	56.2	116.3	113.1
Underwriting, general and administrative expenses	163.0	161.1	331.8	334.4
Interest expense	0.0	0.0	0.0	0.0
Total benefits, losses and expenses	415.3	397.7	842.9	826.6
Segment income (loss) from continuing operations before provision (benefit) for income taxes	119.5	107.6	204.3	201.1
Provision (benefit) for income taxes	25.8	22.2	43.2	41.5
Net income from continuing operations	93.7	85.4	161.1	159.6
Segment assets	3,989.8		3,989.8
Corporate and Other
Revenues
Net earned premiums	0.0	0.0	0.0	0.0
Fees and other income	0.2	0.1	0.4	1.9
Net investment income	9.8	4.8	15.9	11.7
Net realized gains on investments	10.3	28.9	11.1	(55.1)
Total revenues	20.3	33.8	27.4	(41.5)
Benefits, losses and expenses
Policyholder benefits	0.0	0.1	0.0	0.4
Amortization of deferred acquisition costs and value of business acquired	0.0	0.0	0.0	0.0
Underwriting, general and administrative expenses	36.0	63.6	75.7	115.0
Interest expense	28.8	26.7	57.2	52.2
Total benefits, losses and expenses	64.8	90.4	132.9	167.6
Segment income (loss) from continuing operations before provision (benefit) for income taxes	(44.5)	(56.6)	(105.5)	(209.1)
Provision (benefit) for income taxes	(11.7)	(14.1)	(24.7)	(120.1)
Net income from continuing operations	(32.8)	$ (42.5)	(80.8)	$ (89.0)
Segment assets	$ 16,821.7		$ 16,821.7