Basis of Presentation and Significant Accounting Policies Supplemental Cash Flow information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Reduction in Long-term Debt Through Long-term Debt Exchange	$ 71
Income Taxes Paid	8	$ 2
Cash and cash equivalents	23	58	$ 20
Restricted Cash	16	31	13
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	42	91	35	$ 81
Long-term Debt [Member]
Interest Paid, Including Capitalized Interest, Operating and Investing Activities	25	31
Variable Interest Entity, Primary Beneficiary [Member]
Restricted Cash	$ 2	$ 2	$ 2