Segment Information (details) - Assets by Segment (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Assets by segment
Total assets	$ 105,445	$ 104,575
Total reportable segments [Member]
Assets by segment
Total assets	104,935	103,878
Business Insurance [Member]
Assets by segment
Total assets	77,634	76,909
Financial, Professional & International Insurance [Member]
Assets by segment
Total assets	13,620	13,355
Personal Insurance [Member]
Assets by segment
Total assets	13,681	13,614
Other [Member]
Assets by segment
Total assets	$ 510	$ 697