Income Taxes Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions	$ 514	$ 0	$ 0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits as of January 1	0	0	213
Gross decreases- tax positions in prior years	0	0	(213)
Unrecognized tax benefits as of December 31	514	0	$ 0
Unrecognized Tax Benefit Resulting in Tax Credits and/or Net Operating Loss Carryforward	220	$ 0
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 205