Consolidating Financial Statements (details) - Consolidating Statement of Income (Unaudited) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Consolidating Statement of Income
Premiums		$ 6,523	$ 6,209	$ 19,057	$ 18,257
Net investment income		588	582	1,796	1,675
Fee income		113	116	342	352
Net realized investment gains (losses)	[1]	61	23	146	33
Other revenues		40	31	110	115
Total revenues		7,325	6,961	21,451	20,432
Claims and claim adjustment expenses		4,806	3,856	13,125	11,330
Amortization of deferred acquisition costs		1,059	1,012	3,094	2,972
General and administrative expenses		1,045	1,057	3,086	3,106
Interest expense		95	89	276	273
Total claims and expenses		7,005	6,014	19,581	17,681
Income before income taxes		320	947	1,870	2,751
Income tax expense (benefit)		27	231	365	680
Net income		293	716	1,505	2,071
Total other-than-temporary impairment losses		(5)	(4)	(11)	(36)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(5)	(4)	(12)	(26)
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		4,466	4,246	13,039	12,492
Net investment income		405	389	1,218	1,142
Fee income		113	116	342	352
Net realized investment gains (losses)		6	10	(2)	(7)
Other revenues		21	24	75	105
Total revenues		5,011	4,785	14,672	14,084
Claims and claim adjustment expenses		3,191	2,615	8,794	7,710
Amortization of deferred acquisition costs		716	683	2,077	1,999
General and administrative expenses		723	744	2,163	2,191
Interest expense		12	11	36	35
Total claims and expenses		4,642	4,053	13,070	11,935
Income before income taxes		369	732	1,602	2,149
Income tax expense (benefit)		74	194	361	584
Net income		295	538	1,241	1,565
Total other-than-temporary impairment losses		(2)	(1)	(4)	(18)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(2)	(1)	(5)	(13)
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		2,057	1,963	6,018	5,765
Net investment income		189	190	574	524
Net realized investment gains (losses)		56	12	90	39
Other revenues		21	11	42	28
Total revenues		2,323	2,176	6,724	6,356
Claims and claim adjustment expenses		1,615	1,241	4,331	3,620
Amortization of deferred acquisition costs		343	329	1,017	973
General and administrative expenses		314	312	911	923
Total claims and expenses		2,272	1,882	6,259	5,516
Income before income taxes		51	294	465	840
Income tax expense (benefit)		17	81	125	219
Net income		34	213	340	621
Total other-than-temporary impairment losses		(3)	(3)	(7)	(18)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)		(3)	(3)	(7)	(13)
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		7	3	17	9
Net realized investment gains (losses)		(1)		58
Total revenues		6	3	75	9
General and administrative expenses		10	4	19	9
Interest expense		83	78	240	238
Total claims and expenses		93	82	259	247
Income before income taxes		(87)	(79)	(184)	(238)
Income tax expense (benefit)		(60)	(44)	(117)	(123)
Net income of subsidiaries		329	751	1,581	2,186
Net income		302	716	1,514	2,071
Eliminations [Member]
Consolidating Statement of Income
Net investment income		(13)		(13)
Net realized investment gains (losses)			1		1
Other revenues		(2)	(4)	(7)	(18)
Total revenues		(15)	(3)	(20)	(17)
General and administrative expenses		(2)	(3)	(7)	(17)
Total claims and expenses		(2)	(3)	(7)	(17)
Income before income taxes		(13)		(13)
Income tax expense (benefit)		(4)		(4)
Net income of subsidiaries		(329)	(751)	(1,581)	(2,186)
Net income		$ (338)	$ (751)	$ (1,590)	$ (2,186)

[1] Total other-than-temporary impairment (OTTI) losses were $(5) million and $(4) million for the three months ended September 30, 2017 and 2016, respectively, and $(11) million and $(36) million for the nine months ended September 30, 2017 and 2016, respectively. Of total OTTI, credit losses of $(5) million and $(4) million for the three months ended September 30, 2017 and 2016, respectively, and $(12) million and $(26) million for the nine months ended September 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 September 30, 2017 and 2016, and $1 million and $(10) million for the nine months ended September 30, 2017 and 2016, respectively, were recognized in other comprehensive income (loss) as part of changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statement of income.