Fair Value Level 4 (Details) - Fair Value of Debt - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount [Member]
Fair Value of Debt [Line Items]
Debt	$ 1,792	$ 1,785
Debt	1,822	1,815
Fair Value, Inputs, Level 1 [Member]
Fair Value of Debt [Line Items]
Debt	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value of Debt [Line Items]
Debt	1,767	1,751
Fair Value, Inputs, Level 3 [Member]
Fair Value of Debt [Line Items]
Debt	$ 55	$ 64