Income and Other Taxes - Income Tax Expense (Benefit), Current Deferred, by Jurisdiction (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)	$ 7		$ (15)	$ (225)
Deferred Federal Income Tax Expense (Benefit)	411	[1]	(4)	300
Current Foreign Tax Expense	62		71	73
Deferred Foreign Income Tax (Benefit) Expense	(21)		(13)	7
Current State Tax Expense (Benefit)	13		15	(38)
Deferred State Income Tax Expense	9		8	76
Total Provision	$ 481		$ 62	$ 193

[1] Includes $400 estimated impact of the Tax Cuts and Jobs Act (the "Tax Act").