Schedule II (Details) - Condensed Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statement of Comprehensive Income
Net income	$ 873	$ 396	$ 557	$ 796	$ 621	$ 709	$ 524	$ 669	$ 2,622	$ 2,523	$ 2,056
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income									2,994	(1,489)	294
Net changes in benefit plan assets and obligations									33	(56)	29
Other comprehensive income (loss) before income taxes									3,140	(1,819)	522
Income tax expense (benefit)									641	(349)	110
Other comprehensive income (loss), net of taxes, before other comprehensive income (loss) of subsidiaries									2,499	(1,470)	412
Other comprehensive income (loss) of subsidiaries									0	0	0
Other comprehensive income (loss), net of taxes									2,499	(1,470)	412
Comprehensive income									5,121	1,053	2,468
Travelers [Member]
Condensed Statement of Comprehensive Income
Net income									2,622	2,523	2,064
Changes in net unrealized gains on investment securities having no credit losses recognized in the consolidated statement of income									4	0	(44)
Net changes in benefit plan assets and obligations									35	(53)	22
Other comprehensive income (loss) before income taxes									39	(53)	(22)
Income tax expense (benefit)									12	(17)	2
Other comprehensive income (loss), net of taxes, before other comprehensive income (loss) of subsidiaries									27	(36)	(24)
Other comprehensive income (loss) of subsidiaries									2,472	(1,434)	436
Other comprehensive income (loss), net of taxes									2,499	(1,470)	412
Comprehensive income									$ 5,121	$ 1,053	$ 2,476