Shareholders' Equity and Dividend Availability (details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012	May 31, 2013
Shareholders' Equity and Dividend Availability disclosure
Number of authorized shares	1,755
Number of authorized shares, voting common stock	1,745
Number of authorized shares, preferred shares	5			5
Number of authorized shares, undesignated shares	5
Maximum amount of dividends available to be paid by subsidiaries to their parent without prior approval of the Connecticut Insurance Department	$ 3,250,000,000
Number of non-insurance holding companies underneath TRV	2
Dividends received by TRV and its two non-insurance holding companies from their U.S. insurance subsidiaries	4,100,000,000
Cash dividends declared per common share	$ 2.15	$ 1.96	$ 1.79
Cash dividends paid	729,000,000	729,000,000	694,000,000
Statutory net income of the Company's domestic and international insurance subsidiaries	3,970,000,000	4,180,000,000	2,840,000,000
Statutory capital and surplus of the Company's domestic and international insurance subsidiaries	$ 21,050,000,000	$ 21,120,000,000