Income Taxes (Uncertain Tax Positions Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jan. 31, 2018
Income Tax Examination [Line Items]
Income Tax Examination, pre-tax adjustments proposed	$ 192
Income Tax Examination, Estimate of Possible Loss	$ 136
Subsequent Event [Member]
Income Tax Examination [Line Items]
Income Tax Examination, pre-tax adjustments proposed		$ 198