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, 2020	Dec. 31, 2019	Dec. 31, 2018
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total	$ 23	$ 26	$ (3)