Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Operating revenues
Net earned premiums	$ 2,441	$ 2,248
Net investment income	609	525
Non-insurance warranty revenue	407	407
Other revenues	9	7
Total operating revenues	3,466	3,187
Claims, Benefits and Expenses
Net incurred claims and benefits	1,798	1,646
Policyholders’ dividends	9	7
Amortization of deferred acquisition costs	444	379
Non-insurance warranty expense	394	384
Other insurance related expenses	287	305
Other expenses	85	60
Total claims, benefits and expenses	3,017	2,781
Core income (loss) before income tax	449	406
Income tax (expense) benefit on core income (loss)	(94)	(81)
Core income (loss)	355	325
Net investment gains (losses)	(22)	(35)
Income tax (expense) benefit on net investment gains (losses)	5	7
Net investment gains (losses), after tax	(17)	(28)
Net income (loss)	338	297
Operating Segments | Specialty
Operating revenues
Net earned premiums	814	797
Net investment income	150	129
Non-insurance warranty revenue	407	407
Other revenues	1	0
Total operating revenues	1,372	1,333
Claims, Benefits and Expenses
Net incurred claims and benefits	477	465
Policyholders’ dividends	2	1
Amortization of deferred acquisition costs	178	165
Non-insurance warranty expense	394	384
Other insurance related expenses	81	86
Other expenses	15	14
Total claims, benefits and expenses	1,147	1,115
Core income (loss) before income tax	225	218
Income tax (expense) benefit on core income (loss)	(48)	(47)
Core income (loss)	177	171
Operating Segments | Commercial
Operating revenues
Net earned premiums	1,202	1,046
Net investment income	176	149
Non-insurance warranty revenue	0	0
Other revenues	8	7
Total operating revenues	1,386	1,202
Claims, Benefits and Expenses
Net incurred claims and benefits	828	688
Policyholders’ dividends	7	6
Amortization of deferred acquisition costs	200	169
Non-insurance warranty expense	0	0
Other insurance related expenses	138	142
Other expenses	12	6
Total claims, benefits and expenses	1,185	1,011
Core income (loss) before income tax	201	191
Income tax (expense) benefit on core income (loss)	(43)	(40)
Core income (loss)	158	151
Operating Segments | International
Operating revenues
Net earned premiums	315	290
Net investment income	31	23
Non-insurance warranty revenue	0	0
Other revenues	0	0
Total operating revenues	346	313
Claims, Benefits and Expenses
Net incurred claims and benefits	189	189
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	66	45
Non-insurance warranty expense	0	0
Other insurance related expenses	39	47
Other expenses	2	1
Total claims, benefits and expenses	296	282
Core income (loss) before income tax	50	31
Income tax (expense) benefit on core income (loss)	(13)	(7)
Core income (loss)	37	24
Operating Segments | Life & Group
Operating revenues
Net earned premiums	110	115
Net investment income	231	214
Non-insurance warranty revenue	0	0
Other revenues	0	0
Total operating revenues	341	329
Claims, Benefits and Expenses
Net incurred claims and benefits	312	311
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	29	29
Other expenses	0	1
Total claims, benefits and expenses	341	341
Core income (loss) before income tax	0	(12)
Income tax (expense) benefit on core income (loss)	5	9
Core income (loss)	5	(3)
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0
Net investment income	21	10
Non-insurance warranty revenue	0	0
Other revenues	3	3
Total operating revenues	24	13
Claims, Benefits and Expenses
Net incurred claims and benefits	(8)	(7)
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	0	1
Other expenses	59	41
Total claims, benefits and expenses	51	35
Core income (loss) before income tax	(27)	(22)
Income tax (expense) benefit on core income (loss)	5	4
Core income (loss)	(22)	(18)
Eliminations
Operating revenues
Net earned premiums	0	0
Net investment income	0	0
Non-insurance warranty revenue	0	0
Other revenues	(3)	(3)
Total operating revenues	(3)	(3)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0
Policyholders’ dividends	0	0
Amortization of deferred acquisition costs	0	0
Non-insurance warranty expense	0	0
Other insurance related expenses	0	0
Other expenses	(3)	(3)
Total claims, benefits and expenses	(3)	(3)
Core income (loss) before income tax	0	0
Income tax (expense) benefit on core income (loss)	0	0
Core income (loss)	$ 0	$ 0