Retirement and Deferred Compensation Plans (Fair Value of Benefit Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value of Benefit Plans' Assets [Abstract]
Common and preferred stock	$ 615	$ 556
Cash and invested cash	103	120
Other investments	62	58
Total	1,626	1,489
Fixed maturity AFS securities [Member]
Fair Value of Benefit Plans' Assets [Abstract]
Corporate bonds	292	322
U.S. government bonds	291	235
Foreign government bonds	231	167
State and municipal bonds	$ 32	$ 31