Consolidating Financial Statements (Details) - Consolidating Statement of Income (Unaudited) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Consolidating Statement of Income
Premiums		$ 6,988	$ 6,695	$ 13,843	$ 13,232
Net investment income		648	595	1,230	1,198
Fee income		116	112	225	215
Net realized investment gains	[1]	25	36	78	25
Other revenues		57	39	129	93
Total revenues		7,834	7,477	15,505	14,763
Claims and claim adjustment expenses		4,821	4,562	9,263	8,858
Amortization of deferred acquisition costs		1,134	1,081	2,251	2,142
General and administrative expenses		1,125	1,113	2,182	2,175
Interest expense		89	90	177	179
Total claims and expenses		7,169	6,846	13,873	13,354
Income before income taxes		665	631	1,632	1,409
Income tax expense (benefit)		108	107	279	216
Net income of subsidiaries		0	0	0	0
Net income		557	524	1,353	1,193
Total other-than-temporary impairment gains (losses)		(1)	(1)	(2)	(1)
Other-than-temporary impairment losses recognized in net realized investment gains		(1)	(1)	(2)	(1)
Other-than-temporary impairment losses recognized in other comprehensive income (loss)		0	0	0	0
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Income
Premiums		4,786	4,577	9,475	9,045
Net investment income		455	412	871	824
Fee income		116	112	225	215
Net realized investment gains		14	18	36	20
Other revenues		31	13	69	40
Total revenues		5,402	5,132	10,676	10,144
Claims and claim adjustment expenses		3,248	3,064	6,272	5,974
Amortization of deferred acquisition costs		740	727	1,485	1,432
General and administrative expenses		768	766	1,490	1,495
Interest expense		12	13	24	24
Total claims and expenses		4,768	4,570	9,271	8,925
Income before income taxes		634	562	1,405	1,219
Income tax expense (benefit)		122	104	268	210
Net income of subsidiaries		0	0	0	0
Net income		512	458	1,137	1,009
Total other-than-temporary impairment gains (losses)		0	(1)	(1)	(1)
Other-than-temporary impairment losses recognized in net realized investment gains		0	(1)	(1)	(1)
Other-than-temporary impairment losses recognized in other comprehensive income (loss)		0	0	0	0
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Income
Premiums		2,202	2,118	4,368	4,187
Net investment income		181	175	336	360
Fee income		0	0	0	0
Net realized investment gains		6	16	21	4
Other revenues		26	27	60	55
Total revenues		2,415	2,336	4,785	4,606
Claims and claim adjustment expenses		1,573	1,498	2,991	2,884
Amortization of deferred acquisition costs		394	354	766	710
General and administrative expenses		352	343	682	671
Interest expense		0	0	0	0
Total claims and expenses		2,319	2,195	4,439	4,265
Income before income taxes		96	141	346	341
Income tax expense (benefit)		12	21	54	53
Net income of subsidiaries		0	0	0	0
Net income		84	120	292	288
Total other-than-temporary impairment gains (losses)		(1)	0	(1)	0
Other-than-temporary impairment losses recognized in net realized investment gains		(1)	0	(1)	0
Other-than-temporary impairment 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		12	8	23	14
Fee income		0	0	0	0
Net realized investment gains		5	2	21	1
Other revenues		0	0	0	0
Total revenues		17	10	44	15
Claims and claim adjustment expenses		0	0	0	0
Amortization of deferred acquisition costs		0	0	0	0
General and administrative expenses		5	5	10	11
Interest expense		77	77	153	155
Total claims and expenses		82	82	163	166
Income before income taxes		(65)	(72)	(119)	(151)
Income tax expense (benefit)		(26)	(18)	(43)	(47)
Net income of subsidiaries		596	578	1,429	1,297
Net income		557	524	1,353	1,193
Total other-than-temporary impairment gains (losses)		0	0	0	0
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	0	0
Other-than-temporary impairment 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	(1)	0	(2)
Total revenues		0	(1)	0	(2)
Claims and claim adjustment expenses		0	0	0	0
Amortization of deferred acquisition costs		0	0	0	0
General and administrative expenses		0	(1)	0	(2)
Interest expense		0	0	0	0
Total claims and expenses		0	(1)	0	(2)
Income before income taxes		0	0	0	0
Income tax expense (benefit)		0	0	0	0
Net income of subsidiaries		(596)	(578)	(1,429)	(1,297)
Net income		(596)	(578)	(1,429)	(1,297)
Total other-than-temporary impairment gains (losses)		0	0	0	0
Other-than-temporary impairment losses recognized in net realized investment gains		0	0	0	0
Other-than-temporary impairment losses recognized in other comprehensive income (loss)		$ 0	$ 0	$ 0	$ 0

[1] Total other-than-temporary impairment (OTTI) gains (losses) were $(1) million for each of the three months ended June 30, 2019 and 2018, and $(2) million and $(1) million for the six months ended June 30, 2019 and June 30, 2018, respectively.  Of total OTTI, credit losses of $(1) million for each of the three months ended June 30, 2019 and 2018, and $(2) million and $(1) million for the six months ended June 30, 2019 and June 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 six months ended June 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.