Shareholders' Equity (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Comparison of GAAP and statutory net income (loss) [Abstract]
GAAP net income (loss)	$ 452	$ 298	$ 419	$ 509	$ 620	$ 572	$ 518	$ 464	$ 1,678	$ 2,174	$ 2,183
Property and Casualty Insurance Group [Member]
Comparison of GAAP and statutory net income (loss) [Abstract]
GAAP net income (loss)									1,915	2,374	2,324
Statutory net income									1,824	2,295	2,357
Corporate and other [Member]
Comparison of GAAP and statutory net income (loss) [Abstract]
GAAP net income (loss)									$ (237)	$ (200)	$ (141)