Credit Losses (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Credit Loss [Abstract]
Allowance for doubtful accounts		$ 44	$ 22
Accounts Receivable, Credit Loss Expense (Reversal)		44
Accounts Receivable, Allowance for Credit Loss, Writeoff		(22)
Accounts Receivable, Credit Loss Expense (Reversal), CARES Act	$ 30	30	$ 0	$ 0
Accounts Receivable, Allowance For Credit Loss, CARES Act		$ 22