Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets by segment
Total assets	$ 104,602	$ 105,656
Total reportable segments [Member]
Assets by segment
Total assets	103,839	105,049
Business Insurance [Member]
Assets by segment
Total assets	76,870	78,165
Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	13,355	13,461
Personal Insurance [Member]
Assets by segment
Total assets	13,614	13,423
Other [Member]
Assets by segment
Total assets	$ 763	$ 607