Segment Information (details) - Assets by Segment - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Assets by segment
Total assets	$ 100,184	$ 103,078
Reportable Segments [Member]
Assets by segment
Total assets	99,800	102,633
Reportable Segments [Member] | Business and International Insurance [Member]
Assets by segment
Total assets	79,692	82,310
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	7,360	7,525
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	12,748	12,798
Other assets [Member]
Assets by segment
Total assets	$ 384	$ 445