Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating Lease Expense	$ 286	$ 292	$ 0
Finance Lease Expense:
Amortization of ROU assets	11	11
Interest on lease liabilities	21	21
Short Term Lease Expense	6	6
Variable Lease Expense	3	7
Sublease Income	(11)	(15)
Total Lease Expense	$ 316	$ 322