Retirement Plans (Schedule of Components of Net Periodic Benefit Cost (Credit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	$ 1	$ 5	$ 6
Expected return on plan assets	(2)	(9)	(11)
Amortization of net actuarial loss	0	0	1
Settlement loss	28	1	1
Net periodic benefit cost	27	(3)	(3)
Supplemental Employee Retirement Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0	0	0
Expected return on plan assets	0	0	0
Amortization of net actuarial loss	0	0	0
Settlement loss	0	0	0
Net periodic benefit cost	0	0	0
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0	0	0
Expected return on plan assets	0	0	0
Amortization of net actuarial loss	0	0	0
Settlement loss	0	0	0
Net periodic benefit cost	$ 0	$ 0	$ 0