Schedule II (details) - Condensed Income Statements - 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
Condensed Statement of Income
Net investment income										$ 2,397	$ 2,302	$ 2,379
Net realized investment gains (losses)	[1]									216	68	3
Total revenues		$ 7,451	$ 7,325	$ 7,184	$ 6,942	$ 7,193	$ 6,961	$ 6,785	$ 6,686	28,902	27,625	26,815
Interest expense										369	363	373
Expenses, other										4,170	4,154	4,094
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
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
Travelers [Member]
Condensed Statement of Income
Net investment income										24	13	7
Net realized investment gains (losses)										66	(1)	1
Total revenues										90	12	8
Interest expense										321	315	325
Expenses, other										25	5	16
Total claims and expenses										346	320	341
Income before income taxes										(256)	(308)	(333)
Income tax expense (benefit)										(130)	(168)	(108)
Loss before net income of subsidiaries										(126)	(140)	(225)
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

[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.