Credit Facilities Schedule of Short term debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Line of Credit Facility [Abstract]
Average daily amount of short-term debt outstanding	$ 131	$ 7
Weighted daily average interest rate	1.50%	2.60%
Maximum amount outstanding during the year	$ 225	$ 46