Schedule II (Details) - Condensed Statement of Cash Flows - 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 Cash Flows
Net income	$ 1,310	$ 827	$ (40)	$ 600	$ 873	$ 396	$ 557	$ 796	$ 2,697	$ 2,622	$ 2,523
Deferred federal income tax benefit									(29)	(33)	(13)
Other operating activities									129	535	190
Net cash provided by operating activities									6,519	5,205	4,380
Net purchases of short-term securities									(566)	(957)	908
Net cash used in investing activities									(4,892)	(2,902)	(2,329)
Treasury stock acquired — share repurchase authorization									(625)	(1,500)	(1,270)
Treasury stock acquired — net employee share-based compensation									(47)	(48)	(51)
Dividends paid to shareholders									(861)	(844)	(814)
Payment of debt									(500)	(500)	(600)
Issuance of debt									490	492	591
Issuance of common stock -- employee share options									127	213	132
Net cash used in financing activities									(1,416)	(2,187)	(2,012)
Net increase in cash									227	121	29
Cash at beginning of year				494				373	494	373	344
Cash at end of year	721				494				721	494	373
Cash received during the year for taxes									(578)	(428)	(408)
Cash paid during the year for interest									339	338	347
Travelers [Member]
Condensed Statement of Cash Flows
Net income									2,697	2,622	2,523
Equity in net income of subsidiaries									(2,900)	(2,789)	(2,714)
Dividends received from consolidated subsidiaries									1,964	2,459	2,258
Deferred federal income tax benefit									3	(2)	28
Change in income taxes payable									(6)	3	100
Other operating activities									(79)	(79)	(35)
Net cash provided by operating activities									1,679	2,214	2,160
Net purchases of short-term securities									(256)	(19)	(141)
Other investments, net									(7)	(8)	(7)
Net cash used in investing activities									(263)	(27)	(148)
Treasury stock acquired — share repurchase authorization									(625)	(1,500)	(1,270)
Treasury stock acquired — net employee share-based compensation									(47)	(48)	(51)
Dividends paid to shareholders									(861)	(844)	(814)
Payment of debt									(500)	(500)	(600)
Issuance of debt									490	492	591
Issuance of common stock -- employee share options									127	213	132
Net cash used in financing activities									(1,416)	(2,187)	(2,012)
Net increase in cash									0	0	0
Cash at beginning of year				$ 0				$ 0	0	0	0
Cash at end of year	$ 0				$ 0				0	0	0
Cash received during the year for taxes									81	78	283
Cash paid during the year for interest									$ 291	$ 291	$ 300