Benefit Obligations (Schedule of Expense Related to Nonqualified Pension Plans Included in Net Periodic Benefit Cost, Excluding Returns on Assets) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	$ (3)	$ 18	$ 18