Reinsurance (Consolidated Reinsurance) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Premiums written [Abstract]
Direct									$ 19,212	$ 18,144	$ 17,626
Assumed									3,616	3,449	3,205
Ceded									(5,803)	(5,518)	(5,459)
Net									17,025	16,075	15,372
Premiums earned [Abstract]
Direct									18,856	17,802	17,534
Assumed									3,479	3,302	3,349
Ceded									(5,722)	(5,427)	(5,496)
Net premiums earned	$ 4,363	$ 4,610	$ 4,067	$ 3,573	$ 3,848	$ 4,665	$ 3,783	$ 3,381	$ 16,613	$ 15,677	$ 15,387