Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Operating revenues
Net earned premiums	$ 2,593	$ 2,406	$ 7,532	$ 7,001
Net investment income	626	553	1,853	1,653
Non-insurance warranty revenue	401	407	1,212	1,221
Other revenues	8	8	26	22
Total operating revenues	3,628	3,374	10,623	9,897
Claims, Benefits and Expenses
Net incurred claims and benefits	2,010	1,818	5,682	5,236
Policyholders’ dividends	9	8	26	22
Amortization of deferred acquisition costs	457	426	1,336	1,208
Non-insurance warranty expense	387	386	1,169	1,154
Other insurance related expenses	321	294	937	917
Other expenses	69	78	237	197
Total claims, benefits and expenses	3,257	3,010	9,391	8,734
Total claims, benefits and expenses	3,253		9,387
Core income (loss) before income tax	375	364	1,236	1,163
Income tax (expense) benefit on core income (loss)	(82)	(75)	(262)	(241)
Core income (loss)	293	289	974	922
Net investment gains (losses)	(10)	(38)	(42)	(105)
Income tax (expense) benefit on net investment gains (losses)	3	7	9	21
Net investment gains (losses), after tax	(7)	(31)	(33)	(84)
Pension settlement transaction gains (losses)	(4)		(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)	283	258	938	838
Operating Segments | Specialty
Operating revenues
Net earned premiums	848	829	2,493	2,438
Net investment income	157	136	461	407
Non-insurance warranty revenue	401	407	1,212	1,221
Other revenues	1	0	1	0
Total operating revenues	1,407	1,372	4,167	4,066
Claims, Benefits and Expenses
Net incurred claims and benefits	509	480	1,478	1,419
Policyholders’ dividends	2	2	7	5
Amortization of deferred acquisition costs	188	175	546	508
Non-insurance warranty expense	387	386	1,169	1,154
Other insurance related expenses	90	89	267	269
Other expenses	13	13	41	39
Total claims, benefits and expenses		1,145		3,394
Total claims, benefits and expenses	1,189		3,508
Core income (loss) before income tax	218	227	659	672
Income tax (expense) benefit on core income (loss)	(47)	(49)	(142)	(146)
Core income (loss)	171	178	517	526
Operating Segments | Commercial
Operating revenues
Net earned premiums	1,325	1,170	3,774	3,336
Net investment income	183	156	534	470
Non-insurance warranty revenue	0	0	0	0
Other revenues	5	9	23	22
Total operating revenues	1,513	1,335	4,331	3,828
Claims, Benefits and Expenses
Net incurred claims and benefits	954	807	2,628	2,235
Policyholders’ dividends	7	6	19	17
Amortization of deferred acquisition costs	209	188	608	532
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	158	156	454	456
Other expenses	8	11	33	27
Total claims, benefits and expenses		1,168		3,267
Total claims, benefits and expenses	1,336		3,742
Core income (loss) before income tax	177	167	589	561
Income tax (expense) benefit on core income (loss)	(38)	(34)	(125)	(118)
Core income (loss)	139	133	464	443
Operating Segments | International
Operating revenues
Net earned premiums	311	296	937	888
Net investment income	32	26	95	74
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	(1)	0	0
Total operating revenues	343	321	1,032	962
Claims, Benefits and Expenses
Net incurred claims and benefits	195	178	568	552
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	60	63	182	168
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	44	20	129	102
Other expenses	(8)	6	(5)	2
Total claims, benefits and expenses		267		824
Total claims, benefits and expenses	291		874
Core income (loss) before income tax	52	54	158	138
Income tax (expense) benefit on core income (loss)	(16)	(14)	(41)	(36)
Core income (loss)	36	40	117	102
Operating Segments | Life & Group
Operating revenues
Net earned premiums	110	112	329	340
Net investment income	240	216	710	659
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	0	0	0
Total operating revenues	350	328	1,039	999
Claims, Benefits and Expenses
Net incurred claims and benefits	336	343	973	998
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	30	29	88	89
Other expenses	1	(1)	2	0
Total claims, benefits and expenses		371		1,087
Total claims, benefits and expenses	367		1,063
Core income (loss) before income tax	(17)	(43)	(24)	(88)
Income tax (expense) benefit on core income (loss)	8	14	19	36
Core income (loss)	(9)	(29)	(5)	(52)
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	14	19	53	43
Non-insurance warranty revenue	0	0	0	0
Other revenues	3	2	9	7
Total operating revenues	17	21	62	50
Claims, Benefits and Expenses
Net incurred claims and benefits	16	10	35	32
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	0	0	0	0
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	0	1	0	2
Other expenses	56	51	173	136
Total claims, benefits and expenses		62		170
Total claims, benefits and expenses	72		208
Core income (loss) before income tax	(55)	(41)	(146)	(120)
Income tax (expense) benefit on core income (loss)	11	8	27	23
Core income (loss)	(44)	(33)	(119)	(97)
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)	(2)	(7)	(7)
Total operating revenues	(2)	(3)	(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
Other insurance related expenses	(1)	(1)	(1)	(1)
Other expenses	(1)	(2)	(7)	(7)
Total claims, benefits and expenses		(3)		(8)
Total claims, benefits and expenses	(2)		(8)
Core income (loss) before income tax	0	0	0	0
Income tax (expense) benefit on core income (loss)	0	0	0	0
Core income (loss)	$ 0	$ 0	$ 0	$ 0