Income Taxes (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
	Oct. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Impairment Losses, Amount		$ 107
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Amount		2
Deferred Tax Assets, Net, Current		48		$ 55
Income tax refunds		4	$ 35
Subsequent Event [Member]
Income Tax Contingency [Line Items]
Income tax refunds	$ 48
Accounting Stadards Update 2016-09 [Member]
Income Tax Contingency [Line Items]
Current Income Tax Expense (Benefit)		$ 2