Pension and Other Post-Retirement Benefits - Pension and Post-Retirement Plans (Details) - Pension Benefits - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Components of net periodic (credit) expense:
Interest cost	[1]	$ 1	$ 1	$ 2	$ 2
Expected return on plan assets	[1]	(4)	(4)	(8)	(8)
Amortization of net actuarial loss	[1]	2	2	4	4
Net periodic (credit) expense	[1]	$ (1)	$ (1)	$ (2)	$ (2)

[1] Amounts are included in G&A expense on the Consolidated Statements of Income and Comprehensive Income.