Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Assets by segment
Total assets	$ 104,330	$ 104,575
Total reportable segments [Member]
Assets by segment
Total assets	103,986	103,878
Business Insurance [Member]
Assets by segment
Total assets	76,968	76,909
Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	13,491	13,355
Personal Insurance [Member]
Assets by segment
Total assets	13,527	13,614
Other [Member]
Assets by segment
Total assets	$ 344	$ 697