Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Assets by segment
Total assets	$ 102,691	$ 103,078
Reportable Segments [Member]
Assets by segment
Total assets	102,388	102,632
Reportable Segments [Member] | Business and International Insurance [Member]
Assets by segment
Total assets	81,892	82,309
Reportable Segments [Member] | Bond & Specialty Insurance [Member]
Assets by segment
Total assets	7,637	7,525
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	12,859	12,798
Other assets [Member]
Assets by segment
Total assets	$ 303	$ 446