Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Operating revenues
Net earned premiums	$ 2,035	$ 1,850	$ 3,997	$ 3,719
Net investment income	591	534	1,095	863
Non-insurance warranty revenue	359	308	697	609
Other revenues	6	5	11	13
Total operating revenues	2,991	2,697	5,800	5,204
Claims, Benefits and Expenses
Net incurred claims and benefits	1,539	1,636	3,039	3,055
Policyholders’ dividends	7	6	13	12
Amortization of deferred acquisition costs	357	342	716	686
Non-insurance warranty expense	332	285	643	566
Other insurance related expenses	271	260	526	518
Other expenses	61	55	118	127
Total claims, benefits and expenses	2,567	2,584	5,055	4,964
Core income (loss) before income tax	424	113	745	240
Income tax (expense) benefit on core income (loss)	(83)	(14)	(141)	(33)
Core income (loss)	341	99	604	207
Net investment gains (losses)	38	69	95	(147)
Income tax (expense) benefit on net investment gains (losses)	(11)	(17)	(19)	30
Net investment gains (losses), after tax	27	52	76	(117)
Net income (loss)	368	151	680	90
Operating Segments | Specialty
Operating revenues
Net earned premiums	762	705	1,497	1,390
Net investment income	134	133	251	189
Non-insurance warranty revenue	359	308	697	609
Other revenues	0	0	0	1
Total operating revenues	1,255	1,146	2,445	2,189
Claims, Benefits and Expenses
Net incurred claims and benefits	439	508	866	913
Policyholders’ dividends	1	1	2	2
Amortization of deferred acquisition costs	159	153	313	304
Non-insurance warranty expense	332	285	643	566
Other insurance related expenses	71	73	141	142
Other expenses	12	10	23	23
Total claims, benefits and expenses	1,014	1,030	1,988	1,950
Core income (loss) before income tax	241	116	457	239
Income tax (expense) benefit on core income (loss)	(53)	(26)	(99)	(53)
Core income (loss)	188	90	358	186
Operating Segments | Commercial
Operating revenues
Net earned premiums	881	795	1,736	1,613
Net investment income	174	161	322	203
Non-insurance warranty revenue	0	0	0	0
Other revenues	5	5	10	13
Total operating revenues	1,060	961	2,068	1,829
Claims, Benefits and Expenses
Net incurred claims and benefits	588	614	1,227	1,169
Policyholders’ dividends	6	5	11	10
Amortization of deferred acquisition costs	148	147	301	291
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	136	124	251	251
Other expenses	11	12	20	18
Total claims, benefits and expenses	889	902	1,810	1,739
Core income (loss) before income tax	171	59	258	90
Income tax (expense) benefit on core income (loss)	(34)	(10)	(52)	(18)
Core income (loss)	137	49	206	72
Operating Segments | International
Operating revenues
Net earned premiums	266	224	518	463
Net investment income	14	14	28	29
Non-insurance warranty revenue	0	0	0	0
Other revenues	1	0	1	0
Total operating revenues	281	238	547	492
Claims, Benefits and Expenses
Net incurred claims and benefits	159	176	314	330
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	50	42	102	91
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	39	39	74	75
Other expenses	(3)	(2)	(8)	11
Total claims, benefits and expenses	245	255	482	507
Core income (loss) before income tax	36	(17)	65	(15)
Income tax (expense) benefit on core income (loss)	(10)	3	(15)	3
Core income (loss)	26	(14)	50	(12)
Operating Segments | Life & Group
Operating revenues
Net earned premiums	126	126	246	253
Net investment income	265	206	484	414
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	0	0	0
Total operating revenues	390	332	730	667
Claims, Benefits and Expenses
Net incurred claims and benefits	322	304	603	620
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	25	25	50	51
Other expenses	2	0	4	3
Total claims, benefits and expenses	349	329	657	674
Core income (loss) before income tax	41	3	73	(7)
Income tax (expense) benefit on core income (loss)	2	11	6	25
Core income (loss)	43	14	79	18
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	4	20	10	28
Non-insurance warranty revenue	0	0	0	0
Other revenues	2	1	3	2
Total operating revenues	6	21	13	30
Claims, Benefits and Expenses
Net incurred claims and benefits	31	34	29	23
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)	10	(1)
Other expenses	40	36	82	75
Total claims, benefits and expenses	71	69	121	97
Core income (loss) before income tax	(65)	(48)	(108)	(67)
Income tax (expense) benefit on core income (loss)	12	8	19	10
Core income (loss)	(53)	(40)	(89)	(57)
Eliminations
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	0	0	0	0
Non-insurance warranty revenue	0	0	0	0
Other revenues	(1)	(1)	(3)	(3)
Total operating revenues	(1)	(1)	(3)	(3)
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	0	0	0	0
Other expenses	(1)	(1)	(3)	(3)
Total claims, benefits and expenses	(1)	(1)	(3)	(3)
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