Reinsurance (Consolidated Reinsurance) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Premiums written [Abstract]
Direct									$ 20,069	$ 19,212	$ 18,144
Assumed									3,321	3,616	3,449
Ceded									(5,591)	(5,803)	(5,518)
Net									17,799	17,025	16,075
Premiums earned [Abstract]
Direct									19,555	18,856	17,802
Assumed									3,336	3,479	3,302
Ceded									(5,465)	(5,722)	(5,427)
Net premiums earned	$ 4,370	$ 4,754	$ 4,332	$ 3,970	$ 4,363	$ 4,610	$ 4,067	$ 3,573	$ 17,426	$ 16,613	$ 15,677