Pension Plans, Retirement Benefits and Savings Plans (details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jun. 07, 2011
Pension Plans, Retirement Benefits and Savings Plans disclosure
Estimated decrease in prescription drug liabilities expected as a result of the Company's transition to a group-based company-sponsored Medicare Part D Employer Group Waiver Plan (EGWP) program	$ 31
Assumptions used to determine benefit obligations, discount rate (percent)	4.15%	4.90%
Assumptions used to determine benefit obligations, future compensation increase rate (percent)	4.00%	4.00%
Assumptions used to determine net periodic benefit cost, discount rate (percent)	4.90%	5.37%
Assumed health care cost trend rates, following year (percent)	7.50%	8.00%
Assumed health care cost trend rates, rate to which the cost trend rate is assumed to decline (ultimate trend rate) (percent)	5.00%	5.00%
Assumed health care cost trend rates, year that the rate reaches the ultimate trend rate	2018	2018
Impact to accumulated postretirement benefit obligation from increasing the assumed health care cost trend rate by 1%	22
Impact to the aggregate of the serivce and interest cost components of net postretirement benefit expense from increasing the assumed health care cost trend rate by 1%	1
Impact to accumulated postretirement benefit obligation from decreasing the assumed health care cost trend rate by 1%	19
Impact to the aggregate of the serivce and interest cost components of net postretirement benefit expense from decreasing the assumed health care cost trend rate by 1%	1
Savings Plan	The Company has a savings plan, The Travelers 401(k) Savings Plan (the Savings Plan), in which substantially all U.S. domestic Company employees are eligible to participate. Under the Savings Plan, the Company matches employee contributions up to 5% of eligible pay, with a maximum annual match of $5,000 which becomes 100% vested after three years of service. For the year ended December 31, 2011, existing employees whose annual base salary on December 31, 2010 was $175,000 or more, and employees hired during 2011 at an annual base salary of $175,000 or more, were not eligible for the Company's matching contribution. The Company's matching contribution is made in cash and invested according to the employee's current investment elections. The Company's matching contribution can be reinvested at any time into any other investment option. The Company's non-U.S. employees participate in separate savings plans. Included in the Savings Plan are a legacy Savings Plus Plan (SPP) and a Stock Ownership Plan (SOP) in which substantially all employees who were hired by legacy SPC before April 1, 2004 were eligible to participate. In 2004 under the SPP, the Company matched 100% of employees' contributions up to a maximum of 6% of their salary. The match was in the form of preferred shares, to the extent available in the SOP, or in the Company's common shares. Also allocated to participants were preferred shares equal to the value of dividends on previously allocated shares.
Expense related to all savings plans	$ 92	$ 90	$ 94
Annual dividend amount per share of preferred stock		$ 11.72
Number of common shares issued upon conversion of preferred shares, per preferred share				8
Preferred shares outstanding				190,083
Number of common shares issued upon conversion of preferred shares, total				1,520,000