Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Operating revenues
Net earned premiums	$ 1,850	$ 1,824	$ 3,719	$ 3,627
Net investment income	534	515	863	1,086
Non-insurance warranty revenue	308	285	609	566
Other revenues	5	4	13	13
Total operating revenues	2,697	2,628	5,204	5,292
Claims, Benefits and Expenses
Net incurred claims and benefits	1,636	1,346	3,055	2,697
Policyholders’ dividends	6	6	12	12
Amortization of deferred acquisition costs	342	338	686	680
Non-insurance warranty expense	285	263	566	523
Other insurance related expenses	260	258	518	509
Other expenses	55	57	127	123
Total claims, benefits and expenses	2,584	2,268	4,964	4,544
Core income (loss) before income tax	113	360	240	748
Income tax (expense) benefit on core income (loss)	(14)	(66)	(33)	(136)
Core income (loss)	99	294	207	612
Net investment gains (losses)	69	(18)	(147)	13
Income tax (expense) benefit on net investment gains (losses)	(17)	2	30	(5)
Net investment gains (losses), after tax	52	(16)	(117)	8
Net income (loss)	151	278	90	620
Operating Segments | Specialty
Operating revenues
Net earned premiums	705	688	1,390	1,349
Net investment income	133	134	189	289
Non-insurance warranty revenue	308	285	609	566
Other revenues	0	(1)	1	0
Total operating revenues	1,146	1,106	2,189	2,204
Claims, Benefits and Expenses
Net incurred claims and benefits	508	395	913	787
Policyholders’ dividends	1	1	2	2
Amortization of deferred acquisition costs	153	152	304	299
Non-insurance warranty expense	285	263	566	523
Other insurance related expenses	73	76	142	146
Other expenses	10	12	23	24
Total claims, benefits and expenses	1,030	899	1,950	1,781
Core income (loss) before income tax	116	207	239	423
Income tax (expense) benefit on core income (loss)	(26)	(46)	(53)	(93)
Core income (loss)	90	161	186	330
Operating Segments | Commercial
Operating revenues
Net earned premiums	795	763	1,613	1,526
Net investment income	177	154	224	344
Non-insurance warranty revenue	0	0	0	0
Other revenues	5	3	12	10
Total operating revenues	977	920	1,849	1,880
Claims, Benefits and Expenses
Net incurred claims and benefits	666	507	1,224	1,017
Policyholders’ dividends	5	5	10	10
Amortization of deferred acquisition costs	147	130	291	257
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	124	119	251	249
Other expenses	13	7	19	18
Total claims, benefits and expenses	955	768	1,795	1,551
Core income (loss) before income tax	22	152	54	329
Income tax (expense) benefit on core income (loss)	(2)	(32)	(10)	(70)
Core income (loss)	20	120	44	259
Operating Segments | International
Operating revenues
Net earned premiums	224	243	463	493
Net investment income	14	15	29	30
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	1	0	1
Total operating revenues	238	259	492	524
Claims, Benefits and Expenses
Net incurred claims and benefits	176	147	330	309
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	42	56	91	124
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	39	34	75	59
Other expenses	(2)	3	11	7
Total claims, benefits and expenses	255	240	507	499
Core income (loss) before income tax	(17)	19	(15)	25
Income tax (expense) benefit on core income (loss)	3	(2)	3	(2)
Core income (loss)	(14)	17	(12)	23
Operating Segments | Life & Group
Operating revenues
Net earned premiums	126	130	253	260
Net investment income	206	205	414	409
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	0	0	1
Total operating revenues	332	335	667	670
Claims, Benefits and Expenses
Net incurred claims and benefits	304	309	620	617
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	30	51	58
Other expenses	0	2	3	4
Total claims, benefits and expenses	329	341	674	679
Core income (loss) before income tax	3	(6)	(7)	(9)
Income tax (expense) benefit on core income (loss)	11	13	25	26
Core income (loss)	14	7	18	17
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	4	7	7	14
Non-insurance warranty revenue	0	0	0	0
Other revenues	1	2	3	4
Total operating revenues	5	9	10	18
Claims, Benefits and Expenses
Net incurred claims and benefits	(18)	(12)	(32)	(33)
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)	(2)
Other expenses	35	34	74	73
Total claims, benefits and expenses	16	21	41	38
Core income (loss) before income tax	(11)	(12)	(31)	(20)
Income tax (expense) benefit on core income (loss)	0	1	2	3
Core income (loss)	(11)	(11)	(29)	(17)
Eliminations
Operating revenues
Net earned premiums	0	0	0	(1)
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)	(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	0	0	0	(1)
Other expenses	(1)	(1)	(3)	(3)
Total claims, benefits and expenses	(1)	(1)	(3)	(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