Segment Information (details) - Assets by Segment - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Assets by segment
Total assets	$ 102,787	$ 100,184
Reportable Segments [Member]
Assets by segment
Total assets	102,504	99,800
Reportable Segments [Member] | Business and International Insurance [Member]
Assets by segment
Total assets	81,232	79,692
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	7,945	7,360
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	13,327	12,748
Other assets [Member]
Assets by segment
Total assets	$ 283	$ 384