Reinsurance (Consolidated Reinsurance) (Details) - USD ($) $ in Millions	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, 2015	Dec. 31, 2014	Dec. 31, 2013
Premiums written [Abstract]
Direct									$ 19,879	$ 20,069	$ 19,212
Assumed									3,932	3,321	3,616
Ceded									(6,098)	(5,591)	(5,803)
Net									17,713	17,799	17,025
Premiums earned [Abstract]
Direct									19,355	19,555	18,856
Assumed									3,676	3,336	3,479
Ceded									(5,818)	(5,465)	(5,722)
Net premiums earned	$ 4,207	$ 4,719	$ 4,360	$ 3,927	$ 4,370	$ 4,754	$ 4,332	$ 3,970	$ 17,213	$ 17,426	$ 16,613