Business Segments (Income statement information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating revenues
Net earned premiums	$ 2,059	$ 1,953	$ 6,056	$ 5,672
Net investment income	513	517	1,608	1,380
Non-insurance warranty revenue	357	317	1,054	926
Other revenues	8	6	19	19
Total operating revenues	2,937	2,793	8,737	7,997
Claims, Benefits and Expenses
Net incurred claims and benefits	1,627	1,611	4,666	4,666
Policyholders’ dividends	5	5	18	17
Amortization of deferred acquisition costs	368	360	1,084	1,046
Non-insurance warranty expense	330	293	973	859
Other insurance related expenses	253	251	779	769
Other expenses	62	50	180	177
Total claims, benefits and expenses	2,645	2,570	7,700	7,534
Core income (loss) before income tax	292	223	1,037	463
Income tax (expense) benefit on core income (loss)	(55)	(30)	(196)	(63)
Core income (loss)	237	193	841	400
Net investment gains (losses)	22	27	117	(120)
Income tax (expense) benefit on net investment gains (losses)	(3)	(7)	(22)	23
Net investment gains (losses), after tax	19	20	95	(97)
Net income (loss)	256	213	936	303
Operating Segments | Specialty
Operating revenues
Net earned premiums	773	734	2,270	2,124
Net investment income	116	126	367	315
Non-insurance warranty revenue	357	317	1,054	926
Other revenues	1	0	1	1
Total operating revenues	1,247	1,177	3,692	3,366
Claims, Benefits and Expenses
Net incurred claims and benefits	446	433	1,312	1,346
Policyholders’ dividends	0	0	2	2
Amortization of deferred acquisition costs	165	158	478	462
Non-insurance warranty expense	330	293	973	859
Other insurance related expenses	71	66	212	208
Other expenses	13	14	36	37
Total claims, benefits and expenses	1,025	964	3,013	2,914
Core income (loss) before income tax	222	213	679	452
Income tax (expense) benefit on core income (loss)	(49)	(45)	(148)	(98)
Core income (loss)	173	168	531	354
Operating Segments | Commercial
Operating revenues
Net earned premiums	893	857	2,629	2,470
Net investment income	141	151	463	354
Non-insurance warranty revenue	0	0	0	0
Other revenues	7	5	17	18
Total operating revenues	1,041	1,013	3,109	2,842
Claims, Benefits and Expenses
Net incurred claims and benefits	720	671	1,947	1,840
Policyholders’ dividends	5	5	16	15
Amortization of deferred acquisition costs	148	150	449	441
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	125	128	376	379
Other expenses	8	7	28	25
Total claims, benefits and expenses	1,006	961	2,816	2,700
Core income (loss) before income tax	35	52	293	142
Income tax (expense) benefit on core income (loss)	(8)	(11)	(60)	(29)
Core income (loss)	27	41	233	113
Operating Segments | International
Operating revenues
Net earned premiums	271	236	789	699
Net investment income	14	15	42	44
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	0	1	0
Total operating revenues	285	251	832	743
Claims, Benefits and Expenses
Net incurred claims and benefits	171	150	485	480
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	55	52	157	143
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	32	31	106	106
Other expenses	4	(8)	(4)	3
Total claims, benefits and expenses	262	225	744	732
Core income (loss) before income tax	23	26	88	11
Income tax (expense) benefit on core income (loss)	(6)	1	(21)	4
Core income (loss)	17	27	67	15
Operating Segments | Life & Group
Operating revenues
Net earned premiums	123	127	369	380
Net investment income	240	208	724	622
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	0	(1)	0
Total operating revenues	362	335	1,092	1,002
Claims, Benefits and Expenses
Net incurred claims and benefits	296	363	899	983
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	27	28	77	79
Other expenses	1	3	5	6
Total claims, benefits and expenses	324	394	981	1,068
Core income (loss) before income tax	38	(59)	111	(66)
Income tax (expense) benefit on core income (loss)	3	24	9	49
Core income (loss)	41	(35)	120	(17)
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	2	17	12	45
Non-insurance warranty revenue	0	0	0	0
Other revenues	2	1	5	3
Total operating revenues	4	18	17	48
Claims, Benefits and Expenses
Net incurred claims and benefits	(6)	(6)	23	17
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)	9	(2)
Other expenses	37	34	119	109
Total claims, benefits and expenses	30	27	151	124
Core income (loss) before income tax	(26)	(9)	(134)	(76)
Income tax (expense) benefit on core income (loss)	5	1	24	11
Core income (loss)	(21)	(8)	(110)	(65)
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)	0	(4)	(3)
Total operating revenues	(2)	(1)	(5)	(4)
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)	0	(4)	(3)
Total claims, benefits and expenses	(2)	(1)	(5)	(4)
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