Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022		Dec. 31, 2021
Segment Reporting Information [Line Items]
Net written premiums					$ 9,892	$ 9,128		$ 8,405
Operating revenues
Net earned premiums					9,480	8,667	[1]	8,175	[1]
Net investment income					2,264	1,805	[1]	2,159	[1]
Non-insurance warranty revenue					1,624	1,574	[1]	1,430	[1]
Other revenues					30	32	[1]	24	[1]
Total operating revenues					13,398	12,078		11,788
Claims, Benefits and Expenses
Net incurred claims and benefits					7,039	6,628		6,349
Policyholders’ dividends					29	25		22
Amortization of deferred acquisition costs					1,644	1,490	[1]	1,443	[1]
Non-insurance warranty expense					1,544	1,471	[1]	1,328	[1]
Other insurance related expenses					1,251	1,160		1,062
Other expenses					274	291		242
Total claims, benefits and expenses					11,781	11,065	[1]	10,446	[1]
Core income (loss) before income tax					1,617	1,013		1,342
Income tax (expense) benefit on core income (loss)					(333)	(177)		(254)
Core income (loss)	$ 265	$ 43	$ 230	$ 298	1,284	836		1,088
Net investment gains (losses)					(99)	(199)		120
Income tax (expense) benefit on net investment gains (losses)					20	45		(24)
Net investment gains (losses), after tax					(79)	(154)		96
Net income (loss)					1,205	682		1,184
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Net written premiums					3,329	3,306		3,225
Operating revenues
Net earned premiums					3,307	3,203		3,076
Net investment income					558	431		497
Non-insurance warranty revenue					1,624	1,574		1,430
Other revenues					1	1		1
Total operating revenues					5,490	5,209		5,004
Claims, Benefits and Expenses
Net incurred claims and benefits					1,923	1,839		1,787
Policyholders’ dividends					8	6		3
Amortization of deferred acquisition costs					686	656		643
Non-insurance warranty expense					1,544	1,471		1,328
Other insurance related expenses					373	336		296
Other expenses					53	51		47
Total claims, benefits and expenses					4,587	4,359		4,104
Core income (loss) before income tax					903	850		900
Income tax (expense) benefit on core income (loss)					(195)	(182)		(196)
Core income (loss)					708	668		704
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Net written premiums					4,880	4,193		3,595
Operating revenues
Net earned premiums					4,547	3,923		3,552
Net investment income					645	488		624
Non-insurance warranty revenue					0	0		0
Other revenues					29	30		23
Total operating revenues					5,221	4,441		4,199
Claims, Benefits and Expenses
Net incurred claims and benefits					2,995	2,607		2,540
Policyholders’ dividends					21	19		19
Amortization of deferred acquisition costs					729	634		594
Non-insurance warranty expense					0	0		0
Other insurance related expenses					620	557		511
Other expenses					30	36		38
Total claims, benefits and expenses					4,395	3,853		3,702
Core income (loss) before income tax					826	588		497
Income tax (expense) benefit on core income (loss)					(174)	(122)		(103)
Core income (loss)					652	466		394
Operating Segments | International
Segment Reporting Information [Line Items]
Net written premiums					1,237	1,164		1,101
Operating revenues
Net earned premiums					1,176	1,070		1,057
Net investment income					103	63		57
Non-insurance warranty revenue					0	0		0
Other revenues					0	1		0
Total operating revenues					1,279	1,134		1,114
Claims, Benefits and Expenses
Net incurred claims and benefits					722	637		652
Policyholders’ dividends					0	0		0
Amortization of deferred acquisition costs					229	200		206
Non-insurance warranty expense					0	0		0
Other insurance related expenses					139	146		144
Other expenses					(4)	26		(2)
Total claims, benefits and expenses					1,086	1,009		1,000
Core income (loss) before income tax					193	125		114
Income tax (expense) benefit on core income (loss)					(48)	(19)		(28)
Core income (loss)					145	106		86
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Net written premiums					447	467		485
Operating revenues
Net earned premiums					451	473		491
Net investment income					896	804		966
Non-insurance warranty revenue					0	0		0
Other revenues					(1)	(1)		0
Total operating revenues					1,346	1,276		1,457
Claims, Benefits and Expenses
Net incurred claims and benefits					1,317	1,469		1,261
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	118		103
Other expenses					1	9		10
Total claims, benefits and expenses					1,436	1,596		1,374
Core income (loss) before income tax					(90)	(320)		83
Income tax (expense) benefit on core income (loss)					42	99		25
Core income (loss)					(48)	(221)		108
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Net written premiums					0	(1)		0
Operating revenues
Net earned premiums					0	(1)		0
Net investment income					62	19		15
Non-insurance warranty revenue					0	0		0
Other revenues					11	6		6
Total operating revenues					73	24		21
Claims, Benefits and Expenses
Net incurred claims and benefits					82	76		109
Policyholders’ dividends					0	0		0
Amortization of deferred acquisition costs					0	0		0
Non-insurance warranty expense					0	0		0
Other insurance related expenses					2	4		9
Other expenses					204	174		155
Total claims, benefits and expenses					288	254		273
Core income (loss) before income tax					(215)	(230)		(252)
Income tax (expense) benefit on core income (loss)					42	47		48
Core income (loss)					(173)	(183)		(204)
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					(10)	(5)		(6)
Total operating revenues					(11)	(6)		(7)
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					(10)	(5)		(6)
Total claims, benefits and expenses					(11)	(6)		(7)
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

[1] As of January 1, 2023, the Company adopted ASU 2018-12, Financial Services-Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts (ASU 2018-12) using the modified retrospective method applied as of the transition date of January 1, 2021. Prior period amounts in the financial statements have been adjusted to reflect application of the new guidance. See Note A to the Consolidated Financial Statements for additional information.