Segment Information (details) - Assets by Segment - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Assets by segment
Total assets	$ 102,110	$ 103,078
Reportable Segments [Member]
Assets by segment
Total assets	101,679	102,632
Reportable Segments [Member] | Business and International Insurance [Member]
Assets by segment
Total assets	80,905	82,309
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	7,828	7,525
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	12,946	12,798
Other assets [Member]
Assets by segment
Total assets	$ 431	$ 446