Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Assets by segment
Total assets	$ 101,900	$ 104,938
Reportable Segments [Member]
Assets by segment
Total assets	101,382	104,619
Reportable Segments [Member] | Business Insurance [Member]
Assets by segment
Total assets	75,187	76,972
Reportable Segments [Member] | Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	13,035	13,452
Reportable Segments [Member] | Personal Insurance [Member]
Assets by segment
Total assets	13,160	14,195
Interest Expense & Other [Member]
Assets by segment
Total assets	$ 518	$ 319