Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Assets by segment
Total assets	$ 104,134	$ 103,812
Reportable Segments [Member]
Assets by segment
Total assets	103,651	103,307
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	74,225	73,746
Reportable Segments [Member] | Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	16,585	16,691
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	12,841	12,870
Interest Expense & Other [Member]
Assets by segment
Total assets	$ 483	$ 505