Pension and Other Post-Retirement Benefits - Pension and Post-Retirement Plans (Details) - Pension Benefits - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Components of net periodic (credit) expense:
Interest cost	[1]	$ 1	$ 1	$ 3	$ 4
Expected return on plan assets	[1]	(4)	(4)	(12)	(12)
Amortization of net actuarial loss	[1]	2	2	5	5
Net periodic (credit) expense	[1]	$ (1)	$ (1)	$ (4)	$ (3)

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