Insurance Claim Reserves (details) - Prior Year Reserve Development - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	$ 81	$ 180
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	71	93
Bond & Specialty Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	10	60
Personal Insurance [Member]
Liability for claims and claim adjustment expense
Net favorable prior year reserve development impacting the Company's results of operations	$ 0	$ 27