Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
Net written premiums	$ 9,128	$ 8,405	$ 8,059
Operating revenues
Net earned premiums	8,667	8,175	7,649
Net investment income	1,805	2,159	1,935
Non-insurance warranty revenue	1,574	1,430	1,252
Other revenues	32	24	26
Total operating revenues	12,078	11,788	10,862
Claims, Benefits and Expenses
Net incurred claims and benefits	6,361	6,327	6,149
Policyholders’ dividends	25	22	21
Amortization of deferred acquisition costs	1,490	1,443	1,410
Non-insurance warranty expense	1,471	1,328	1,159
Other insurance related expenses	1,160	1,062	1,028
Other expenses	291	242	220
Total claims, benefits and expenses	10,798	10,424	9,987
Core income (loss) before income tax	1,280	1,364	875
Income tax (expense) benefit on core income (loss)	(232)	(258)	(140)
Core income (loss)	1,048	1,106	735
Net investment gains (losses)	(199)	120	(54)
Income tax (expense) benefit on net investment gains (losses)	45	(24)	9
Net investment gains (losses), after tax	(154)	96	(45)
Net income (loss)	894	1,202	690
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Net written premiums	3,306	3,225	3,040
Operating revenues
Net earned premiums	3,203	3,076	2,883
Net investment income	431	497	449
Non-insurance warranty revenue	1,574	1,430	1,252
Other revenues	1	1	1
Total operating revenues	5,209	5,004	4,585
Claims, Benefits and Expenses
Net incurred claims and benefits	1,839	1,787	1,792
Policyholders’ dividends	6	3	3
Amortization of deferred acquisition costs	656	643	621
Non-insurance warranty expense	1,471	1,328	1,159
Other insurance related expenses	336	296	280
Other expenses	51	47	50
Total claims, benefits and expenses	4,359	4,104	3,905
Core income (loss) before income tax	850	900	680
Income tax (expense) benefit on core income (loss)	(182)	(196)	(145)
Core income (loss)	668	704	535
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Net written premiums	4,193	3,595	3,565
Operating revenues
Net earned premiums	3,923	3,552	3,323
Net investment income	488	624	513
Non-insurance warranty revenue	0	0	0
Other revenues	30	23	25
Total operating revenues	4,441	4,199	3,861
Claims, Benefits and Expenses
Net incurred claims and benefits	2,607	2,540	2,375
Policyholders’ dividends	19	19	18
Amortization of deferred acquisition costs	634	594	592
Non-insurance warranty expense	0	0	0
Other insurance related expenses	557	511	506
Other expenses	36	38	34
Total claims, benefits and expenses	3,853	3,702	3,525
Core income (loss) before income tax	588	497	336
Income tax (expense) benefit on core income (loss)	(122)	(103)	(69)
Core income (loss)	466	394	267
Operating Segments | International
Segment Reporting Information [Line Items]
Net written premiums	1,164	1,101	961
Operating revenues
Net earned premiums	1,070	1,057	940
Net investment income	63	57	58
Non-insurance warranty revenue	0	0	0
Other revenues	1	0	0
Total operating revenues	1,134	1,114	998
Claims, Benefits and Expenses
Net incurred claims and benefits	637	652	629
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	200	206	197
Non-insurance warranty expense	0	0	0
Other insurance related expenses	146	144	136
Other expenses	26	(2)	(7)
Total claims, benefits and expenses	1,009	1,000	955
Core income (loss) before income tax	125	114	43
Income tax (expense) benefit on core income (loss)	(19)	(28)	(5)
Core income (loss)	106	86	38
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Net written premiums	467	485	494
Operating revenues
Net earned premiums	473	491	504
Net investment income	804	966	851
Non-insurance warranty revenue	0	0	0
Other revenues	(1)	0	0
Total operating revenues	1,276	1,457	1,355
Claims, Benefits and Expenses
Net incurred claims and benefits	1,202	1,239	1,286
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	118	103	109
Other expenses	9	10	7
Total claims, benefits and expenses	1,329	1,352	1,402
Core income (loss) before income tax	(53)	105	(47)
Income tax (expense) benefit on core income (loss)	44	21	56
Core income (loss)	(9)	126	9
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Net written premiums	(1)	0	0
Operating revenues
Net earned premiums	(1)	0	0
Net investment income	19	15	64
Non-insurance warranty revenue	0	0	0
Other revenues	6	6	5
Total operating revenues	24	21	69
Claims, Benefits and Expenses
Net incurred claims and benefits	76	109	67
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	4	9	(2)
Other expenses	174	155	141
Total claims, benefits and expenses	254	273	206
Core income (loss) before income tax	(230)	(252)	(137)
Income tax (expense) benefit on core income (loss)	47	48	23
Core income (loss)	(183)	(204)	(114)
Eliminations
Segment Reporting Information [Line Items]
Net written premiums	(1)	(1)	(1)
Operating revenues
Net earned premiums	(1)	(1)	(1)
Net investment income	0	0	0
Non-insurance warranty revenue	0	0	0
Other revenues	(5)	(6)	(5)
Total operating revenues	(6)	(7)	(6)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0	0
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	(1)	(1)	(1)
Other expenses	(5)	(6)	(5)
Total claims, benefits and expenses	(6)	(7)	(6)
Core income (loss) before income tax	0	0	0
Income tax (expense) benefit on core income (loss)	0	0	0
Core income (loss)	$ 0	$ 0	$ 0