Income Taxes (Reconciliation of Provision for Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Expected provision (benefit) at federal statutory rate	$ 273	$ 400	$ (5)
Increase (decrease) resulting from:
State income taxes, net of federal income tax effect	18	39	0
Change in valuation allowance	(526)	(392)	2
Return to accrual	(16)	0	0
Federal research and development credit	(13)	0	0
Other	7	4	3
Provision (Benefit) for Income Taxes	$ (257)	$ 51	$ 0