Segment Information - Financial Information by Segment (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | segment			3
Revenues
Net earned premiums	$ 2,140.1	$ 2,086.8	$ 6,396.3	$ 6,173.6
Fees and other income	309.6	209.4	858.0	829.4
Net investment income	76.0	63.3	235.2	212.3
Net realized gains (losses) on investments	112.1	17.2	123.2	(37.9)
Total revenues	2,637.8	2,376.7	7,612.7	7,177.4
Benefits, losses and expenses
Policyholder benefits	614.2	638.5	1,681.2	1,697.3
Amortization of deferred acquisition costs and value of business acquired	965.6	927.3	2,903.7	2,689.6
Underwriting, general and administrative expenses	818.3	672.9	2,301.2	2,290.9
Interest expense	27.5	25.5	84.7	77.7
Loss on extinguishment of debt (Note 10)	20.7	0.0	20.7	0.0
Total benefits, losses and expenses	2,446.3	2,264.2	6,991.5	6,755.5
Segment income (loss) from continuing operations before provision (benefit) for income taxes	191.5	112.5	621.2	421.9
Provision (benefit) for income taxes	37.9	24.5	134.4	20.6
Net income from continuing operations	153.6	88.0	486.8	401.3
Net income (loss) from discontinued operations	728.8	(118.5)	762.0	(97.6)
Net income (loss)	882.4	(30.5)	1,248.8	303.7
Less: Net loss (income) attributable to non-controlling interests	0.0	0.3	0.0	(1.1)
Net income (loss) attributable to stockholders	882.4	(30.2)	1,248.8	302.6
Less: Preferred stock dividends	0.0	(4.7)	(4.7)	(14.0)
Net income (loss) attributable to common stockholders	882.4	(34.9)	1,244.1	288.6
Net income (loss) attributable to common stockholders	882.4	(34.9)	1,244.1	288.6
Segment assets	33,624.8		33,624.8		$ 44,649.9
Global Lifestyle
Revenues
Net earned premiums	1,688.5	1,633.2	5,014.6	4,799.0
Fees and other income	274.5	171.8	748.5	721.6
Net investment income	48.5	44.6	148.7	143.5
Net realized gains (losses) on investments	0.0	0.0	0.0	0.0
Total revenues	2,011.5	1,849.6	5,911.8	5,664.1
Benefits, losses and expenses
Policyholder benefits	335.1	365.4	1,007.3	1,044.7
Amortization of deferred acquisition costs and value of business acquired	910.0	870.5	2,731.8	2,519.7
Underwriting, general and administrative expenses	614.6	480.8	1,690.0	1,649.4
Interest expense	0.0	0.0	0.0	0.0
Loss on extinguishment of debt (Note 10)	0.0		0.0
Total benefits, losses and expenses	1,859.7	1,716.7	5,429.1	5,213.8
Segment income (loss) from continuing operations before provision (benefit) for income taxes	151.8	132.9	482.7	450.3
Provision (benefit) for income taxes	27.8	26.3	105.8	101.0
Net income from continuing operations	124.0	106.6	376.9	349.3
Segment assets	25,425.3		25,425.3
Global Housing
Revenues
Net earned premiums	451.6	453.6	1,381.7	1,374.6
Fees and other income	35.1	37.7	109.1	106.0
Net investment income	20.2	16.5	63.3	54.9
Net realized gains (losses) on investments	0.0	0.0	0.0	0.0
Total revenues	506.9	507.8	1,554.1	1,535.5
Benefits, losses and expenses
Policyholder benefits	279.1	272.8	673.9	651.9
Amortization of deferred acquisition costs and value of business acquired	55.6	56.8	171.9	169.9
Underwriting, general and administrative expenses	169.5	162.2	501.3	496.6
Interest expense	0.0	0.0	0.0	0.0
Loss on extinguishment of debt (Note 10)	0.0		0.0
Total benefits, losses and expenses	504.2	491.8	1,347.1	1,318.4
Segment income (loss) from continuing operations before provision (benefit) for income taxes	2.7	16.0	207.0	217.1
Provision (benefit) for income taxes	(0.5)	2.9	42.7	44.4
Net income from continuing operations	3.2	13.1	164.3	172.7
Segment assets	4,285.2		4,285.2
Corporate and Other
Revenues
Net earned premiums	0.0	0.0	0.0	0.0
Fees and other income	0.0	(0.1)	0.4	1.8
Net investment income	7.3	2.2	23.2	13.9
Net realized gains (losses) on investments	112.1	17.2	123.2	(37.9)
Total revenues	119.4	19.3	146.8	(22.2)
Benefits, losses and expenses
Policyholder benefits	0.0	0.3	0.0	0.7
Amortization of deferred acquisition costs and value of business acquired	0.0	0.0	0.0	0.0
Underwriting, general and administrative expenses	34.2	29.9	109.9	144.9
Interest expense	27.5	25.5	84.7	77.7
Loss on extinguishment of debt (Note 10)	20.7		20.7
Total benefits, losses and expenses	82.4	55.7	215.3	223.3
Segment income (loss) from continuing operations before provision (benefit) for income taxes	37.0	(36.4)	(68.5)	(245.5)
Provision (benefit) for income taxes	10.6	(4.7)	(14.1)	(124.8)
Net income from continuing operations	26.4	$ (31.7)	(54.4)	$ (120.7)
Segment assets	$ 3,914.3		$ 3,914.3