Contingencies, Commitments and Guarantees (details) (USD $)	7 Months Ended	9 Months Ended	12 Months Ended
	Apr. 30, 2002 item	Sep. 30, 2012 item	Dec. 31, 2005 item	Apr. 27, 2012 item	Jan. 24, 2012	Dec. 31, 2011	Jul. 26, 2011	Mar. 18, 2011	Oct. 25, 2010 item
Contingencies and Commitments disclosure
Number of purported class action suits filed against TPC and other insurers in state court in West Virginia relative to asbestos direct action litigation	2
Maximum lump-sum payment included in the settlement reached in November 2003 relative to Statutory and Hawaii Actions		$ 412,000,000
Maximum payment required under May 2004 settlement resolving substantially all pending and similar future Common Law Claims relative to Statutory and Hawaii Actions		90,000,000
Number of putative class action lawsuits brought against a number of insurers relative to broker anti-trust litigation			4
Amount Company has agreed to pay under broker anti-trust litigation settlement								6,750,000
Number of settlement class members appealing the court's order granting final approval of the settlement regarding the broker anti-trust litigation				3
Number of other reinsurers beside American Re against which judgment was entered in a reinsurance dispute									3
Judgment amount awarded to Company in reinsurance dispute					251,000,000				251,000,000
Pre-judgment interest amount awarded to Company in reinsurance dispute									169,000,000
Total judgment amount awarded to Company in reinsurance dispute		493,000,000			467,000,000
Total pre- and post-judgment interest amount accrued in reinsurance dispute					216,000,000
Post-judgment interest rate accruing on judgment against non-settling defendants		9.00%
Preliminary class settlement amount approved by court in workers' compensation matter, amount payable by defendants							450,000,000
Number of parties who objected to the settlement and filed notices of appeal in workers' compensation matter		3
Preliminary class settlement amount approved by court in workers' compensation matter, anticipated amount allocable to Company		90,000,000
Unfunded commitments to private equity limited partnerships and real estate partnerships		$ 1,220,000,000				$ 1,150,000,000