Insurance Claim Reserves (details) - Prior Year Reserve Development by Segment - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	$ 941	$ 941	$ 840
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	405	322	399
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
Bond & Specialty Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	258	450	232
Personal Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	$ 278	$ 169	$ 209