Segment Information (details) - Assets by Segment - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Assets by segment
Total assets	$ 101,680	$ 100,184
Reportable Segments [Member]
Assets by segment
Total assets	101,403	99,800
Reportable Segments [Member] | Business and International Insurance [Member]
Assets by segment
Total assets	80,961	79,692
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	7,537	7,360
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	12,905	12,748
Other assets [Member]
Assets by segment
Total assets	$ 277	$ 384