Income Taxes (Schedule of Statutory Federal Income Tax Rate Reconciles to Actual Income Tax Expense (Benefit)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense at statutory federal rate	$ 141	$ 221	$ 240
State income taxes including credits, net	21	34	40
Other nondeductible expenses	8	13	15
Nontaxable income	(32)	(28)	(24)
Share-based compensation	(1)	(4)	(7)
Tax credits and other taxes	(4)	1	(5)
Total	$ 133	$ 237	$ 259