Schedule II (Details) - Condensed Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Statement of Comprehensive Income
Net income	$ 621	$ 709	$ 524	$ 669	$ 551	$ 293	$ 595	$ 617	$ 2,523	$ 2,056	$ 3,014
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income									(1,489)	294	(883)
Net changes in benefit plan assets and obligations									(56)	29	16
Other comprehensive income (loss) before income taxes									(1,819)	522	(887)
Income tax expense (benefit)									(349)	110	(289)
Other comprehensive income (loss), net of taxes, before other comprehensive income (loss) of subsidiaries									(1,470)	412	(598)
Other comprehensive income (loss), net of taxes									(1,470)	412	(598)
Comprehensive income									1,053	2,468	2,416
Travelers [Member]
Condensed Statement of Comprehensive Income
Net income									2,523	2,064	3,014
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income										(44)	11
Net changes in benefit plan assets and obligations									(53)	22	(20)
Other comprehensive income (loss) before income taxes									(53)	(22)	(9)
Income tax expense (benefit)									(17)	2	(1)
Other comprehensive income (loss), net of taxes, before other comprehensive income (loss) of subsidiaries									(36)	(24)	(8)
Other comprehensive income (loss) of subsidiaries									(1,434)	436	(590)
Other comprehensive income (loss), net of taxes									(1,470)	412	(598)
Comprehensive income									$ 1,053	$ 2,476	$ 2,416