Consolidating Financial Statements (details) - Consolidating Statement of Income (Unaudited) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Consolidating Statement of Income
Premiums		$ 6,351	$ 6,067	$ 12,534	$ 12,048
Net investment income		598	549	1,208	1,093
Fee income		116	119	229	236
Net realized investment gains (losses)	[1]	80	19	85	10
Other revenues		39	31	70	84
Total revenues		7,184	6,785	14,126	13,471
Claims and claim adjustment expenses		4,225	3,762	8,319	7,474
Amortization of deferred acquisition costs		1,032	989	2,035	1,960
General and administrative expenses		1,045	1,054	2,041	2,049
Interest expense		92	93	181	184
Total claims and expenses		6,394	5,898	12,576	11,667
Income before income taxes		790	887	1,550	1,804
Income tax expense (benefit)		195	223	338	449
Net income		595	664	1,212	1,355
Total other-than-temporary impairment losses		(5)	(4)	(6)	(32)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(5)	(4)	(7)	(22)
Other-than-temporary impairment gains (losses) recognized in other comprehensive income		0	0	1	(10)
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Income
Premiums		4,345	4,161	8,573	8,246
Net investment income		401	377	813	753
Fee income		116	119	229	236
Net realized investment gains (losses)		(4)	(1)	(8)	(17)
Other revenues		30	33	54	81
Total revenues		4,888	4,689	9,661	9,299
Claims and claim adjustment expenses		2,851	2,575	5,603	5,095
Amortization of deferred acquisition costs		693	666	1,361	1,316
General and administrative expenses		737	743	1,440	1,447
Interest expense		12	12	24	24
Total claims and expenses		4,293	3,996	8,428	7,882
Income before income taxes		595	693	1,233	1,417
Income tax expense (benefit)		157	191	287	390
Net income		438	502	946	1,027
Total other-than-temporary impairment losses		(2)	(3)	(2)	(17)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(2)	(3)	(3)	(12)
Other-than-temporary impairment gains (losses) recognized in other comprehensive income				1	(5)
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Income
Premiums		2,006	1,906	3,961	3,802
Net investment income		191	168	385	334
Net realized investment gains (losses)		25	20	34	27
Other revenues		12	1	21	17
Total revenues		2,234	2,095	4,401	4,180
Claims and claim adjustment expenses		1,374	1,187	2,716	2,379
Amortization of deferred acquisition costs		339	323	674	644
General and administrative expenses		305	313	597	611
Total claims and expenses		2,018	1,823	3,987	3,634
Income before income taxes		216	272	414	546
Income tax expense (benefit)		54	69	108	138
Net income		162	203	306	408
Total other-than-temporary impairment losses		(3)	(1)	(4)	(15)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(3)	(1)	(4)	(10)
Other-than-temporary impairment gains (losses) recognized in other comprehensive income					(5)
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Income
Net investment income		6	4	10	6
Net realized investment gains (losses)		59		59
Total revenues		65	4	69	6
General and administrative expenses		6	1	9	5
Interest expense		80	81	157	160
Total claims and expenses		86	82	166	165
Income before income taxes		(21)	(78)	(97)	(159)
Income tax expense (benefit)		(16)	(37)	(57)	(79)
Net income of subsidiaries		600	705	1,252	1,435
Net income		595	664	1,212	1,355
Eliminations [Member]
Consolidating Statement of Income
Other revenues		(3)	(3)	(5)	(14)
Total revenues		(3)	(3)	(5)	(14)
General and administrative expenses		(3)	(3)	(5)	(14)
Total claims and expenses		(3)	(3)	(5)	(14)
Net income of subsidiaries		(600)	(705)	(1,252)	(1,435)
Net income		$ (600)	$ (705)	$ (1,252)	$ (1,435)

[1] Total other-than-temporary impairment (OTTI) losses were $(5) million and $(4) million for the three months ended June 30, 2017 and 2016, respectively, and $(6) million and $(32) million for the six months ended June 30, 2017 and 2016, respectively. Of total OTTI, credit losses of $(5) million and $(4) million for the three months ended June 30, 2017 and 2016, respectively, and $(7) million and $(22) million for the six months ended June 30, 2017 and 2016, 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 ended June 30, 2017 and 2016, and $1 million and $(10) million for the six months ended June 30, 2017 and 2016, respectively, were recognized in other comprehensive income as part of changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income.