Segment Information (details) - Assets by Segment (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Assets by segment
Total assets	$ 106,933	$ 105,656
Total reportable segments
Assets by segment
Total assets	106,366	105,049
Business Insurance
Assets by segment
Total assets	78,434	78,165
Financial, Professional & International Insurance
Assets by segment
Total assets	13,721	13,461
Personal Insurance
Assets by segment
Total assets	14,211	13,423
Other
Assets by segment
Total assets	$ 567	$ 607