Schedule II (Details) - Condensed Statement of Cash Flows - 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 Cash Flows
Net income	$ 873	$ 396	$ 557	$ 796	$ 621	$ 709	$ 524	$ 669	$ 2,622	$ 2,523	$ 2,056
Equity in net income of subsidiaries									0	0	0
Deferred federal income tax expense (benefit)									(33)	(13)	337
Other operating activities									535	190	43
Net cash provided by operating activities									5,205	4,380	4,148
Net sales (purchases) of short-term securities									(957)	908	(26)
Acquisition, net of cash acquired									0	(4)	(439)
Net cash used in investing activities									(2,902)	(2,329)	(2,202)
Treasury stock acquired — share repurchase authorization									(1,500)	(1,270)	(1,378)
Treasury stock acquired — net employee share-based compensation									(48)	(51)	(62)
Dividends paid to shareholders									(844)	(814)	(785)
Payment of debt									(500)	(600)	(657)
Issuance of debt									492	591	789
Issuance of common stock -- employee share options									213	132	173
Net cash used in financing activities									(2,187)	(2,012)	(1,920)
Net increase in cash									121	29	37
Cash at beginning of year				373				344	373	344	307
Cash at end of year	494				373				494	373	344
Cash received during the year for taxes									(428)	(408)	(514)
Cash paid during the year for interest									338	347	367
Travelers [Member]
Condensed Statement of Cash Flows
Net income									2,622	2,523	2,064
Equity in net income of subsidiaries									(2,789)	(2,714)	(2,190)
Dividends received from consolidated subsidiaries									2,459	2,258	2,289
Deferred federal income tax expense (benefit)									(2)	28	40
Change in income taxes payable									3	100	3
Other operating activities									(79)	(35)	(174)
Net cash provided by operating activities									2,214	2,160	2,032
Net sales (purchases) of short-term securities									(19)	(141)	397
Other investments, net									(8)	(7)	(34)
Acquisition, net of cash acquired									0	0	(477)
Net cash used in investing activities									(27)	(148)	(114)
Treasury stock acquired — share repurchase authorization									(1,500)	(1,270)	(1,378)
Treasury stock acquired — net employee share-based compensation									(48)	(51)	(62)
Dividends paid to shareholders									(844)	(814)	(785)
Payment of debt									(500)	(600)	(657)
Issuance of debt									492	591	789
Issuance of common stock -- employee share options									213	132	173
Net cash used in financing activities									(2,187)	(2,012)	(1,920)
Net increase in cash									0	0	(2)
Cash at beginning of year				$ 0				$ 0	0	0	2
Cash at end of year	$ 0				$ 0				0	0	0
Cash received during the year for taxes									78	283	173
Cash paid during the year for interest									$ 291	$ 300	$ 320