Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Operating revenues
Net earned premiums	$ 2,783	$ 2,593	$ 8,103	$ 7,532
Net investment income	638	626	1,904	1,853
Non-insurance warranty revenue	393	401	1,188	1,212
Other revenues	10	8	28	26
Total operating revenues	3,824	3,628	11,223	10,623
Claims, Benefits and Expenses
Net incurred claims and benefits	2,023	2,010	6,115	5,682
Policyholders’ dividends	9	9	29	26
Amortization of deferred acquisition costs	483	457	1,423	1,336
Non-insurance warranty expense	377	387	1,146	1,169
Insurance related administrative expenses	324	321	982	937
Interest expense	36	32	99	101
Other expenses	52	37	125	136
Total claims, benefits and expenses	3,304	3,253	9,919	9,387
Income tax (expense) benefit on core income (loss)	(111)	(82)	(279)	(262)
Core income (loss)	409	293	1,025	974
Net investment gains (losses)	(7)	(10)	(62)	(42)
Income tax (expense) benefit on net investment gains (losses)	1	3	13	9
Net investment gains (losses), after tax	(6)	(7)	(49)	(33)
Pension settlement transaction gains (losses)	0	(4)	0	(4)
Income tax (expense) benefit on pension settlement transaction gains (losses)		1		1
Pension settlement transaction gains (losses), after tax		(3)		(3)
Net income (loss)	403	283	976	938
Operating Segments | Specialty
Operating revenues
Net earned premiums	881	848	2,573	2,493
Net investment income	162	157	483	461
Non-insurance warranty revenue	393	401	1,188	1,212
Other revenues	1	1	1	1
Total operating revenues	1,437	1,407	4,245	4,167
Claims, Benefits and Expenses
Net incurred claims and benefits	534	509	1,562	1,478
Policyholders’ dividends	2	2	7	7
Amortization of deferred acquisition costs	197	188	581	546
Non-insurance warranty expense	377	387	1,146	1,169
Insurance related administrative expenses	88	90	268	267
Interest expense	0	0	0	0
Other expenses	16	13	41	41
Total claims, benefits and expenses	1,214	1,189	3,605	3,508
Income tax (expense) benefit on core income (loss)	(47)	(47)	(137)	(142)
Core income (loss)	176	171	503	517
Operating Segments | Commercial
Operating revenues
Net earned premiums	1,453	1,325	4,235	3,774
Net investment income	192	183	575	534
Non-insurance warranty revenue	0	0	0	0
Other revenues	8	5	26	23
Total operating revenues	1,653	1,513	4,836	4,331
Claims, Benefits and Expenses
Net incurred claims and benefits	960	954	2,907	2,628
Policyholders’ dividends	7	7	22	19
Amortization of deferred acquisition costs	215	209	645	608
Non-insurance warranty expense	0	0	0	0
Insurance related administrative expenses	165	158	498	454
Interest expense	0	0	0	0
Other expenses	11	8	36	33
Total claims, benefits and expenses	1,358	1,336	4,108	3,742
Income tax (expense) benefit on core income (loss)	(62)	(38)	(153)	(125)
Core income (loss)	233	139	575	464
Operating Segments | International
Operating revenues
Net earned premiums	344	311	978	937
Net investment income	42	32	114	95
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	0	0	0
Total operating revenues	386	343	1,092	1,032
Claims, Benefits and Expenses
Net incurred claims and benefits	203	195	590	568
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	71	60	197	182
Non-insurance warranty expense	0	0	0	0
Insurance related administrative expenses	42	44	125	129
Interest expense	0	0	0	0
Other expenses	(1)	(8)	(12)	(5)
Total claims, benefits and expenses	315	291	900	874
Income tax (expense) benefit on core income (loss)	(24)	(16)	(55)	(41)
Core income (loss)	47	36	137	117
Operating Segments | Life & Group
Operating revenues
Net earned premiums	106	110	318	329
Net investment income	226	240	687	710
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	0	0	0
Total operating revenues	332	350	1,005	1,039
Claims, Benefits and Expenses
Net incurred claims and benefits	336	336	949	973
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Insurance related administrative expenses	29	30	90	88
Interest expense	0	0	0	0
Other expenses	0	1	1	2
Total claims, benefits and expenses	365	367	1,040	1,063
Income tax (expense) benefit on core income (loss)	11	8	20	19
Core income (loss)	(22)	(9)	(15)	(5)
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	16	14	45	53
Non-insurance warranty revenue	0	0	0	0
Other revenues	2	3	8	9
Total operating revenues	18	17	53	62
Claims, Benefits and Expenses
Net incurred claims and benefits	(10)	16	107	35
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Insurance related administrative expenses	1	0	2	0
Interest expense	36	32	99	101
Other expenses	27	24	66	72
Total claims, benefits and expenses	54	72	274	208
Income tax (expense) benefit on core income (loss)	11	11	46	27
Core income (loss)	(25)	(44)	(175)	(119)
Eliminations
Operating revenues
Net earned premiums	(1)	(1)	(1)	(1)
Net investment income	0	0	0	0
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	(1)	(7)	(7)
Total operating revenues	(2)	(2)	(8)	(8)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0	0	0
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Insurance related administrative expenses	(1)	(1)	(1)	(1)
Interest expense	0	0	0	0
Other expenses	(1)	(1)	(7)	(7)
Total claims, benefits and expenses	(2)	(2)	(8)	(8)
Income tax (expense) benefit on core income (loss)	0	0	0	0
Core income (loss)	$ 0	$ 0	$ 0	$ 0