Income Tax (Provision for Income Tax from Continuing Operations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 368	$ (374)	$ 35
Foreign	18	4	0
Subtotal	386	(370)	35
Deferred:
Federal	(1,124)	(1,320)	212
Foreign	0	0	0
Subtotal	(1,124)	(1,320)	212
Current and Deferred
Provision for income tax expense (benefit)	$ (738)	$ (1,690)	$ 247