Income Taxes (Components of Income Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Federal, current	$ 454	$ 871	$ 927
State, current	51	71	33
Total current	505	942	960
Federal, deferred	(474)	301	320
State, deferred	71	25	84
Total deferred	(403)	326	404
Income Tax Expense (Benefit), Total	$ 102	$ 1,268	$ 1,364