Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating revenues
Net earned premiums	$ 1,953	$ 1,890	$ 5,672	$ 5,517
Net investment income	517	487	1,380	1,573
Non-insurance warranty revenue	317	292	926	858
Other revenues	6	9	19	22
Total operating revenues	2,793	2,678	7,997	7,970
Claims, Benefits and Expenses
Net incurred claims and benefits	1,611	1,607	4,666	4,304
Policyholders’ dividends	5	7	17	19
Amortization of deferred acquisition costs	360	345	1,046	1,025
Non-insurance warranty expense	293	278	859	801
Other insurance related expenses	251	257	769	766
Other expenses	50	64	177	187
Total claims, benefits and expenses	2,570	2,558	7,534	7,102
Core income (loss) before income tax	223	120	463	868
Income tax (expense) benefit on core income (loss)	(30)	(18)	(63)	(154)
Core income (loss)	193	102	400	714
Net investment gains (losses)	27	7	(120)	20
Income tax (expense) benefit on net investment gains (losses)	(7)	(2)	23	(7)
Net investment gains (losses), after tax	20	5	(97)	13
Net income (loss)	213	107	303	727
Operating Segments | Specialty
Operating revenues
Net earned premiums	734	712	2,124	2,061
Net investment income	126	121	315	410
Non-insurance warranty revenue	317	292	926	858
Other revenues	0	1	1	1
Total operating revenues	1,177	1,126	3,366	3,330
Claims, Benefits and Expenses
Net incurred claims and benefits	433	411	1,346	1,198
Policyholders’ dividends	0	2	2	4
Amortization of deferred acquisition costs	158	155	462	454
Non-insurance warranty expense	293	278	859	801
Other insurance related expenses	66	71	208	217
Other expenses	14	13	37	37
Total claims, benefits and expenses	964	930	2,914	2,711
Core income (loss) before income tax	213	196	452	619
Income tax (expense) benefit on core income (loss)	(45)	(43)	(98)	(136)
Core income (loss)	168	153	354	483
Operating Segments | Commercial
Operating revenues
Net earned premiums	857	813	2,470	2,339
Net investment income	165	136	389	480
Non-insurance warranty revenue	0	0	0	0
Other revenues	6	10	18	20
Total operating revenues	1,028	959	2,877	2,839
Claims, Benefits and Expenses
Net incurred claims and benefits	673	564	1,897	1,581
Policyholders’ dividends	5	5	15	15
Amortization of deferred acquisition costs	150	134	441	391
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	127	123	378	372
Other expenses	7	9	26	27
Total claims, benefits and expenses	962	835	2,757	2,386
Core income (loss) before income tax	66	124	120	453
Income tax (expense) benefit on core income (loss)	(14)	(27)	(24)	(97)
Core income (loss)	52	97	96	356
Operating Segments | International
Operating revenues
Net earned premiums	236	236	699	729
Net investment income	15	17	44	47
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	(1)	0	0
Total operating revenues	251	252	743	776
Claims, Benefits and Expenses
Net incurred claims and benefits	150	163	480	472
Policyholders’ dividends	0	0	0	0
Amortization of deferred acquisition costs	52	56	143	180
Non-insurance warranty expense	0	0	0	0
Other insurance related expenses	31	35	106	94
Other expenses	(8)	7	3	14
Total claims, benefits and expenses	225	261	732	760
Core income (loss) before income tax	26	(9)	11	16
Income tax (expense) benefit on core income (loss)	1	0	4	(2)
Core income (loss)	27	(9)	15	14
Operating Segments | Life & Group
Operating revenues
Net earned premiums	127	130	380	390
Net investment income	208	207	622	616
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	(1)	0	0
Total operating revenues	335	336	1,002	1,006
Claims, Benefits and Expenses
Net incurred claims and benefits	363	476	983	1,093
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	28	29	79	87
Other expenses	3	1	6	5
Total claims, benefits and expenses	394	506	1,068	1,185
Core income (loss) before income tax	(59)	(170)	(66)	(179)
Income tax (expense) benefit on core income (loss)	24	48	49	74
Core income (loss)	(35)	(122)	(17)	(105)
Operating Segments | Corporate & Other
Operating revenues
Net earned premiums	0	0	0	0
Net investment income	3	6	10	20
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	1	3	5
Total operating revenues	3	7	13	25
Claims, Benefits and Expenses
Net incurred claims and benefits	(8)	(7)	(40)	(40)
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	(1)	(2)
Other expenses	34	35	108	108
Total claims, benefits and expenses	26	28	67	66
Core income (loss) before income tax	(23)	(21)	(54)	(41)
Income tax (expense) benefit on core income (loss)	4	4	6	7
Core income (loss)	(19)	(17)	(48)	(34)
Eliminations
Operating revenues
Net earned premiums	(1)	(1)	(1)	(2)
Net investment income	0	0	0	0
Non-insurance warranty revenue	0	0	0	0
Other revenues	0	(1)	(3)	(4)
Total operating revenues	(1)	(2)	(4)	(6)
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)	(2)
Other expenses	0	(1)	(3)	(4)
Total claims, benefits and expenses	(1)	(2)	(4)	(6)
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