Schedule II (Details) - Condensed Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statement of Comprehensive Income
Net income	$ 1,310	$ 827	$ (40)	$ 600	$ 873	$ 396	$ 557	$ 796	$ 2,697	$ 2,622	$ 2,523
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income									2,331	2,994	(1,489)
Net changes in benefit plan assets and obligations									18	33	(56)
Other comprehensive income (loss) before income taxes									2,352	3,140	(1,819)
Income tax expense (benefit)									490	641	(349)
Other comprehensive income (loss), net of taxes									1,862	2,499	(1,470)
Comprehensive income									4,559	5,121	1,053
Travelers [Member]
Condensed Statement of Comprehensive Income
Net income									2,697	2,622	2,523
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income									3	4	0
Net changes in benefit plan assets and obligations									25	35	(53)
Other comprehensive income (loss) before income taxes									28	39	(53)
Income tax expense (benefit)									9	12	(17)
Other comprehensive income (loss), net of taxes, before other comprehensive income (loss) of subsidiaries									19	27	(36)
Other comprehensive income (loss) of subsidiaries									1,843	2,472	(1,434)
Other comprehensive income (loss), net of taxes									1,862	2,499	(1,470)
Comprehensive income									$ 4,559	$ 5,121	$ 1,053