Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Assets by segment
Total assets	$ 104,866	$ 104,602
Total reportable segments [Member]
Assets by segment
Total assets	104,341	103,839
Business Insurance [Member]
Assets by segment
Total assets	77,299	76,870
Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	13,547	13,355
Personal Insurance [Member]
Assets by segment
Total assets	13,495	13,614
Other [Member]
Assets by segment
Total assets	$ 525	$ 763