Insurance Claim Reserves (details) - Prior Year Reserve Development by Segment (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	$ 941	$ 840	$ 940
Reportable Segments [Member] | Business and International Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	322	399	585
Increase to net favorable prior year reserve development related to workers' compensation reinsurance pool for accident years 1996 and prior	162
Reduction to net favorable prior year reserve development precipitated by legislation in New York related to the New York Fund for Reopened Cases for workers' compensation		42
Reduction to net favorable prior year reserve development due to interest awarded as part of damages relating to a legal matter	77
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	450	232	180
Reportable Segments [Member] | Personal Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	$ 169	$ 209	$ 175