Income Taxes - U.S. Federal Statutory Income Tax Rate Reconciled to Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Pre-Tax Income	$ 270	$ 241	$ 200
Tax Expense/(Benefit)
U.S. federal statutory tax rate	57	51	70
State income taxes, net of federal benefit	20	18	10
Tax rate change	0	0	(40)
Nondeductible meals, entertainment and penalties	1	1	1
Stock based compensation	(1)	(9)	(15)
Uncertain tax positions	0	1	4
Tax credits	(7)	(5)	(4)
State and tax return to provision adjustments	(8)	(7)	(5)
Sec 199 benefits	(1)	0	(3)
Other	(3)	(1)	4
Total	$ 58	$ 49	$ 22
Percent of Pre-Tax Income (Loss)
U.S. federal statutory tax rate	21.00%	21.00%	35.00%
State income taxes, net of federal benefit	7.00%	8.00%	5.00%
Tax rate change	0.00%	0.00%	(20.00%)
Nondeductible meals, entertainment and penalties	0.00%	0.00%	0.00%
Stock based compensation	0.00%	(4.00%)	(7.00%)
Uncertain tax positions	0.00%	0.00%	2.00%
Tax credits	(3.00%)	(2.00%)	(2.00%)
State and tax return to provision adjustments	(3.00%)	(3.00%)	(3.00%)
Sec 199 benefits	0.00%	0.00%	(1.00%)
Other	(1.00%)	0.00%	2.00%
Total	21.00%	20.00%	11.00%