Long-term Debt and Interest Expense (Interest Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Disclosure [Abstract]
Cash payments for interest	$ 102	$ 117	$ 133
Accretion of finance lease	17	4	0
Amortization of issuance discounts	29	1	1
Amortization of capitalized loan fees	5	4	4
Net changes in accruals	(19)	0	(6)
Interest incurred	134	126	132
Less capitalized interest	(5)	(5)	(6)
Total interest expense	129	121	126
Debt Instrument [Line Items]
Interest expense	$ 51	$ 9	$ 5