Business Segments (Income Statement Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net written premiums	$ 8,405	$ 8,059	$ 7,656
Operating revenues
Net earned premiums	8,175	7,649	7,428
Net investment income	2,159	1,935	2,118
Non-insurance warranty revenue	1,430	1,252	1,161
Other revenues	24	26	31
Total operating revenues	11,788	10,862	10,738
Claims, Benefits and Expenses
Net incurred claims and benefits	6,327	6,149	5,783
Policyholders’ dividends	22	21	23
Amortization of deferred acquisition costs	1,443	1,410	1,383
Non-insurance warranty expense	1,328	1,159	1,082
Other insurance related expenses	1,062	1,028	1,038
Other expenses	242	220	235
Total claims, benefits and expenses	10,424	9,987	9,544
Core income (loss) before income tax	1,364	875	1,194
Income tax (expense) benefit on core income (loss)	(258)	(140)	(215)
Core income (loss)	1,106	735	979
Net investment gains (losses)	120	(54)	29
Income tax (expense) benefit on net investment gains (losses)	(24)	9	(8)
Net investment gains (losses), after tax	96	(45)	21
Net income (loss)	1,202	690	1,000
Operating Segments | Specialty
Segment Reporting Information [Line Items]
Net written premiums	3,225	3,040	2,848
Operating revenues
Net earned premiums	3,076	2,883	2,773
Net investment income	497	449	556
Non-insurance warranty revenue	1,430	1,252	1,161
Other revenues	1	1	1
Total operating revenues	5,004	4,585	4,491
Claims, Benefits and Expenses
Net incurred claims and benefits	1,787	1,792	1,595
Policyholders’ dividends	3	3	5
Amortization of deferred acquisition costs	643	621	610
Non-insurance warranty expense	1,328	1,159	1,082
Other insurance related expenses	296	280	292
Other expenses	47	50	48
Total claims, benefits and expenses	4,104	3,905	3,632
Core income (loss) before income tax	900	680	859
Income tax (expense) benefit on core income (loss)	(196)	(145)	(188)
Core income (loss)	704	535	671
Operating Segments | Commercial
Segment Reporting Information [Line Items]
Net written premiums	3,595	3,565	3,315
Operating revenues
Net earned premiums	3,552	3,323	3,162
Net investment income	624	513	605
Non-insurance warranty revenue	0	0	0
Other revenues	23	25	29
Total operating revenues	4,199	3,861	3,796
Claims, Benefits and Expenses
Net incurred claims and benefits	2,540	2,375	2,086
Policyholders’ dividends	19	18	18
Amortization of deferred acquisition costs	594	592	537
Non-insurance warranty expense	0	0	0
Other insurance related expenses	511	506	505
Other expenses	38	34	32
Total claims, benefits and expenses	3,702	3,525	3,178
Core income (loss) before income tax	497	336	618
Income tax (expense) benefit on core income (loss)	(103)	(69)	(138)
Core income (loss)	394	267	480
Operating Segments | International
Segment Reporting Information [Line Items]
Net written premiums	1,101	961	971
Operating revenues
Net earned premiums	1,057	940	974
Net investment income	57	58	63
Non-insurance warranty revenue	0	0	0
Other revenues	0	0	0
Total operating revenues	1,114	998	1,037
Claims, Benefits and Expenses
Net incurred claims and benefits	652	629	624
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	206	197	236
Non-insurance warranty expense	0	0	0
Other insurance related expenses	144	136	130
Other expenses	(2)	(7)	8
Total claims, benefits and expenses	1,000	955	998
Core income (loss) before income tax	114	43	39
Income tax (expense) benefit on core income (loss)	(28)	(5)	(9)
Core income (loss)	86	38	30
Operating Segments | Life & Group
Segment Reporting Information [Line Items]
Net written premiums	485	494	523
Operating revenues
Net earned premiums	491	504	520
Net investment income	966	851	820
Non-insurance warranty revenue	0	0	0
Other revenues	0	0	0
Total operating revenues	1,457	1,355	1,340
Claims, Benefits and Expenses
Net incurred claims and benefits	1,239	1,286	1,416
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	103	109	115
Other expenses	10	7	8
Total claims, benefits and expenses	1,352	1,402	1,539
Core income (loss) before income tax	105	(47)	(199)
Income tax (expense) benefit on core income (loss)	21	56	90
Core income (loss)	126	9	(109)
Operating Segments | Corporate & Other
Segment Reporting Information [Line Items]
Net written premiums	0	0	1
Operating revenues
Net earned premiums	0	0	1
Net investment income	15	64	74
Non-insurance warranty revenue	0	0	0
Other revenues	6	5	6
Total operating revenues	21	69	81
Claims, Benefits and Expenses
Net incurred claims and benefits	109	67	62
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	9	(2)	(2)
Other expenses	155	141	144
Total claims, benefits and expenses	273	206	204
Core income (loss) before income tax	(252)	(137)	(123)
Income tax (expense) benefit on core income (loss)	48	23	30
Core income (loss)	(204)	(114)	(93)
Eliminations
Segment Reporting Information [Line Items]
Net written premiums	(1)	(1)	(2)
Operating revenues
Net earned premiums	(1)	(1)	(2)
Net investment income	0	0	0
Non-insurance warranty revenue	0	0	0
Other revenues	(6)	(5)	(5)
Total operating revenues	(7)	(6)	(7)
Claims, Benefits and Expenses
Net incurred claims and benefits	0	0	0
Policyholders’ dividends	0	0	0
Amortization of deferred acquisition costs	0	0	0
Non-insurance warranty expense	0	0	0
Other insurance related expenses	(1)	(1)	(2)
Other expenses	(6)	(5)	(5)
Total claims, benefits and expenses	(7)	(6)	(7)
Core income (loss) before income tax	0	0	0
Income tax (expense) benefit on core income (loss)	0	0	0
Core income (loss)	$ 0	$ 0	$ 0