Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets by segment
Total assets	$ 102,685	$ 104,938
Reportable Segments [Member]
Assets by segment
Total assets	102,188	104,619
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	74,931	76,972
Reportable Segments [Member] | Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	14,084	13,452
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	13,173	14,195
Interest Expense & Other [Member]
Assets by segment
Total assets	$ 497	$ 319