Schedule II (Details) - Condensed Statement of Cash Flows - 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 Cash Flows
Net income	$ 621	$ 709	$ 524	$ 669	$ 551	$ 293	$ 595	$ 617	$ 2,523	$ 2,056	$ 3,014
Deferred federal income tax expense									(13)	337	110
Other operating activities									190	43	456
Net cash provided by operating activities									4,380	4,148	4,469
Net sales (purchases) of short-term securities									908	(26)	(199)
Acquisition, net of cash acquired									(4)	(439)
Net cash used in investing activities									(2,329)	(2,202)	(1,727)
Treasury stock acquired — share repurchase authorization									(1,270)	(1,378)	(2,400)
Treasury stock acquired — net employee share-based compensation									(51)	(62)	(72)
Dividends paid to shareholders									(814)	(785)	(757)
Payment of debt									(600)	(657)	(400)
Issuance of debt									591	789	491
Issuance of common stock -- employee share options									132	173	332
Net cash used in financing activities									(2,012)	(1,920)	(2,806)
Net increase (decrease) in cash									29	37	(73)
Cash at beginning of year				$ 344				307	344	307	380
Cash at end of year	$ 373				$ 344				373	344	307
Cash received during the year for taxes									(408)	(514)	(892)
Cash paid during the year for interest									347	367	358
Travelers [Member]
Condensed Statement of Cash Flows
Net income									2,523	2,064	3,014
Equity in net income of subsidiaries									(2,714)	(2,190)	(3,154)
Dividends received from consolidated subsidiaries									2,258	2,289	2,998
Deferred federal income tax expense									28	40	12
Change in income taxes payable									100	3	(48)
Other operating activities									(35)	(174)	70
Net cash provided by operating activities									2,160	2,032	2,892
Net sales (purchases) of short-term securities									(141)	397	(81)
Other investments, net									(7)	(34)	(5)
Acquisition, net of cash acquired										(477)
Net cash used in investing activities									(148)	(114)	(86)
Treasury stock acquired — share repurchase authorization									(1,270)	(1,378)	(2,400)
Treasury stock acquired — net employee share-based compensation									(51)	(62)	(72)
Dividends paid to shareholders									(814)	(785)	(757)
Payment of debt									(600)	(657)	(400)
Issuance of debt									591	789	491
Issuance of common stock -- employee share options									132	173	332
Net cash used in financing activities									(2,012)	(1,920)	(2,806)
Net increase (decrease) in cash										(2)
Cash at beginning of year								$ 2		2	2
Cash at end of year											2
Cash received during the year for taxes									283	173	132
Cash paid during the year for interest									$ 300	$ 320	$ 311