Insurance Claim Reserves (details) - Prior Year Reserve Development by Segment (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Prior year reserve development by segment
Net favorable prior year reserve development impacting the Company's results of operations	$ 940	$ 715	$ 1,250
Business Insurance [Member]
Prior year reserve development by segment
Net favorable prior year reserve development impacting the Company's results of operations	467	245	901
Financial, Professional & International Insurance [Member]
Prior year reserve development by segment
Net favorable prior year reserve development impacting the Company's results of operations	298	360	259
Personal Insurance [Member]
Prior year reserve development by segment
Net favorable prior year reserve development impacting the Company's results of operations	$ 175	$ 110	$ 87