Consolidating Financial Statements (details) - Consolidating Statement of Income (Unaudited) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Consolidating Statement of Income
Premiums										$ 25,683	$ 24,534	$ 23,874
Net investment income										2,397	2,302	2,379
Fee income										447	458	460
Net realized investment gains (losses)	[1]									216	68	3
Other revenues										159	263	99
Total revenues		$ 7,451	$ 7,325	$ 7,184	$ 6,942	$ 7,193	$ 6,961	$ 6,785	$ 6,686	28,902	27,625	26,815
Claims and claim adjustment expenses										17,467	15,070	13,723
Amortization of deferred acquisition costs										4,166	3,985	3,885
General and administrative expenses										4,170	4,154	4,094
Interest expense										369	363	373
Total claims and expenses		6,591	7,005	6,394	6,182	5,891	6,014	5,898	5,769	26,172	23,572	22,075
Income before income taxes		860	320	790	760	1,302	947	887	917	2,730	4,053	4,740
Income tax expense (benefit)		309	27	195	143	359	231	223	226	674	1,039	1,301
Net income		$ 551	$ 293	$ 595	$ 617	$ 943	$ 716	$ 664	$ 691	2,056	3,014	3,439
Total other-than-temporary impairment losses										(13)	(40)	(54)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)										(14)	(29)	(52)
Other-than-temporary impairment losses recognized in other comprehensive income (loss)											(11)	(2)
Other-than-temporary impairment gains recognized in other comprehensive income (loss)										1
Travelers [Member]
Consolidating Statement of Income
Net investment income										24	13	7
Net realized investment gains (losses)										66	(1)	1
Total revenues										90	12	8
General and administrative expenses										25	5	16
Interest expense										321	315	325
Total claims and expenses										346	320	341
Income before income taxes										(256)	(308)	(333)
Income tax expense (benefit)										(130)	(168)	(108)
Net income of subsidiaries										2,190	3,154	3,664
Net income										2,064	3,014	3,439
Other-than-temporary impairment losses recognized in net realized investment gains (losses)										0	(1)	0
Other-than-temporary impairment losses recognized in other comprehensive income (loss)										0	0	0
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Income
Premiums										17,562	16,788	16,254
Net investment income										1,627	1,569	1,612
Fee income										447	458	460
Net realized investment gains (losses)										19	30	13
Other revenues										101	248	78
Total revenues										19,756	19,093	18,417
Claims and claim adjustment expenses										11,735	10,232	9,208
Amortization of deferred acquisition costs										2,820	2,702	2,627
General and administrative expenses										2,906	2,928	2,853
Interest expense										48	48	48
Total claims and expenses										17,509	15,910	14,736
Income before income taxes										2,247	3,183	3,681
Income tax expense (benefit)										519	999	1,015
Net income										1,728	2,184	2,666
Total other-than-temporary impairment losses										(4)	(19)	(19)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)										(5)	(13)	(18)
Other-than-temporary impairment losses recognized in other comprehensive income (loss)											(6)	(1)
Other-than-temporary impairment gains recognized in other comprehensive income (loss)										1
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Income
Premiums										8,121	7,746	7,620
Net investment income										759	720	760
Net realized investment gains (losses)										131	39	(11)
Other revenues										68	36	21
Total revenues										9,079	8,541	8,390
Claims and claim adjustment expenses										5,732	4,838	4,515
Amortization of deferred acquisition costs										1,346	1,283	1,258
General and administrative expenses										1,249	1,242	1,225
Total claims and expenses										8,327	7,363	6,998
Income before income taxes										752	1,178	1,392
Income tax expense (benefit)										290	208	394
Net income										462	970	998
Total other-than-temporary impairment losses										(9)	(20)	(35)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)										(9)	(15)	(34)
Other-than-temporary impairment losses recognized in other comprehensive income (loss)											(5)	(1)
Reportable Legal Entities [Member] | Travelers [Member]
Consolidating Statement of Income
Net investment income										24	13	7
Net realized investment gains (losses)										66	(1)	1
Total revenues										90	12	8
General and administrative expenses										25	5	16
Interest expense										321	315	325
Total claims and expenses										346	320	341
Income before income taxes										(256)	(308)	(333)
Income tax expense (benefit)										(130)	(168)	(108)
Net income of subsidiaries										2,190	3,154	3,664
Net income										2,064	3,014	3,439
Total other-than-temporary impairment losses											(1)
Other-than-temporary impairment losses recognized in net realized investment gains (losses)											(1)
Eliminations [Member]
Consolidating Statement of Income
Net investment income										(13)
Other revenues										(10)	(21)
Total revenues										(23)	(21)
General and administrative expenses										(10)	(21)
Total claims and expenses										(10)	(21)
Income before income taxes										(13)
Income tax expense (benefit)										(5)
Net income of subsidiaries										(2,190)	(3,154)	(3,664)
Net income										$ (2,198)	$ (3,154)	$ (3,664)

[1] Total other-than-temporary impairment (OTTI) losses were $(13) million, $(40) million and $(54) million for the years ended December 31, 2017, 2016 and 2015, respectively. Of total OTTI, credit losses of $(14) million, $(29) million and $(52) million for the years ended December 31, 2017, 2016 and 2015, respectively, were recognized in net realized investment gains. In addition, unrealized gains (losses) from other changes in total OTTI of $1 million, $(11) million and $(2) million for the years ended December 31, 2017, 2016 and 2015, 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 statements of income.