Consolidating Financial Statements (Details) - Consolidating Statement of Income (Unaudited) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Consolidating Statement of Income
Premiums		$ 7,179	$ 6,882	$ 21,022	$ 20,114
Net investment income		622	646	1,852	1,844
Fee income		121	109	346	324
Net realized investment gains	[1]	23	29	101	54
Other revenues		68	57	197	150
Total revenues		8,013	7,723	23,518	22,486
Claims and claim adjustment expenses		5,230	4,655	14,493	13,513
Amortization of deferred acquisition costs		1,169	1,117	3,420	3,259
General and administrative expenses		1,098	1,059	3,280	3,234
Interest expense		84	86	261	265
Total claims and expenses		7,581	6,917	21,454	20,271
Income before income taxes		432	806	2,064	2,215
Income tax expense (benefit)		36	97	315	313
Net income of subsidiaries		0	0	0	0
Net income		396	709	1,749	1,902
Total other-than-temporary impairment losses		0	0	(2)	(1)
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	(2)	(1)
Other-than-temporary impairment gains (losses) recognized in other comprehensive income (loss)		0	0	0	0
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Income
Premiums		4,923	4,715	14,398	13,760
Net investment income		428	444	1,299	1,268
Fee income		120	108	345	323
Net realized investment gains		7	13	43	33
Other revenues		36	29	105	69
Total revenues		5,514	5,309	16,190	15,453
Claims and claim adjustment expenses		3,555	3,149	9,827	9,123
Amortization of deferred acquisition costs		791	757	2,276	2,189
General and administrative expenses		752	728	2,242	2,223
Interest expense		12	12	36	36
Total claims and expenses		5,110	4,646	14,381	13,571
Income before income taxes		404	663	1,809	1,882
Income tax expense (benefit)		42	104	310	314
Net income of subsidiaries		0	0	0	0
Net income		362	559	1,499	1,568
Total other-than-temporary impairment losses		0	0	(1)	(1)
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	(1)	(1)
Other-than-temporary impairment gains (losses) recognized in other comprehensive income (loss)		0	0	0	0
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Income
Premiums		2,256	2,167	6,624	6,354
Net investment income		185	193	521	553
Fee income		1	1	1	1
Net realized investment gains		16	9	37	13
Other revenues		32	30	92	85
Total revenues		2,490	2,400	7,275	7,006
Claims and claim adjustment expenses		1,675	1,506	4,666	4,390
Amortization of deferred acquisition costs		378	360	1,144	1,070
General and administrative expenses		341	326	1,023	997
Interest expense		0	0	0	0
Total claims and expenses		2,394	2,192	6,833	6,457
Income before income taxes		96	208	442	549
Income tax expense (benefit)		12	36	66	89
Net income of subsidiaries		0	0	0	0
Net income		84	172	376	460
Total other-than-temporary impairment losses		0	0	(1)	0
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	(1)	0
Other-than-temporary impairment gains (losses) recognized in other comprehensive income (loss)		0	0	0	0
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Income
Premiums		0	0	0	0
Net investment income		9	9	32	23
Fee income		0	0	0	0
Net realized investment gains		0	7	21	8
Other revenues		0	0	0	0
Total revenues		9	16	53	31
Claims and claim adjustment expenses		0	0	0	0
Amortization of deferred acquisition costs		0	0	0	0
General and administrative expenses		5	7	15	18
Interest expense		72	74	225	229
Total claims and expenses		77	81	240	247
Income before income taxes		(68)	(65)	(187)	(216)
Income tax expense (benefit)		(18)	(43)	(61)	(90)
Net income of subsidiaries		446	731	1,875	2,028
Net income		396	709	1,749	1,902
Total other-than-temporary impairment losses		0	0	0	0
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	0	0
Other-than-temporary impairment gains (losses) recognized in other comprehensive income (loss)		0	0	0	0
Eliminations [Member]
Consolidating Statement of Income
Premiums		0	0	0	0
Net investment income		0	0	0	0
Fee income		0	0	0	0
Net realized investment gains		0	0	0	0
Other revenues		0	(2)	0	(4)
Total revenues		0	(2)	0	(4)
Claims and claim adjustment expenses		0	0	0	0
Amortization of deferred acquisition costs		0	0	0	0
General and administrative expenses		0	(2)	0	(4)
Interest expense		0	0	0	0
Total claims and expenses		0	(2)	0	(4)
Income before income taxes		0	0	0	0
Income tax expense (benefit)		0	0	0	0
Net income of subsidiaries		(446)	(731)	(1,875)	(2,028)
Net income		(446)	(731)	(1,875)	(2,028)
Total other-than-temporary impairment losses		0	0	0	0
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	0	0
Other-than-temporary impairment gains (losses) recognized in other comprehensive income (loss)		$ 0	$ 0	$ 0	$ 0

[1] Total other-than-temporary impairment (OTTI) losses were $0 million for each of the three months ended September 30, 2019 and 2018, and $(2) million and $(1) million for the nine months ended September 30, 2019 and September 30, 2018, respectively.  Of total OTTI, credit losses of $0 million for each of the three months ended September 30, 2019 and 2018, and $(2) million and $(1) million for the nine months ended September 30, 2019 and September 30, 2018, respectively, were recognized in net realized investment gains.  In addition, unrealized gains (losses) from other changes in total OTTI of $0 million for each of the three months and nine months ended September 30, 2019 and 2018 were recognized in other comprehensive income (loss) as part of changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income.