Letters of Credit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 250	$ 0
Letter of Credit
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 2	$ 2
Letter of Credit
Line of Credit Facility [Line Items]
Line of Credit Facility, Expiration Period	1 year