Income Taxes - Income Tax Expense Reconciled to Tax Computed at Statutory Rates (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Expense
Federal Income Taxes	$ 762	$ 906		$ 904
State Income Taxes	117	108		112
Other	(17)	(29)		(21)
Total Income Tax Expense	$ 862	$ 985	[1]	$ 995	[1]
Rate
Federal Income Taxes	21.00%	21.00%		21.00%
State Income Taxes	3.20%	2.50%		2.60%
Other	(0.40%)	(0.70%)		(0.50%)
Income Tax Rate	23.80%	22.80%		23.10%

[1] Certain prior year data has been reclassified to conform to the current presentation.