Income Taxes Unrecognized Benefits (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Unrecognized tax benefit - Permanent tax positions	$ 4	$ 3
Unrecognized tax benefit - Temporary tax positions	4	4
Total unrecognized tax benefit	8	7
NOL and tax credit carryforwards	7	6
Reasonably possible decrease in unrecognized tax benefits	5
Unrecognized Tax Benefits, Interest on Income Taxes Accrued	(1)	(1)	$ 1
Unrecognized Tax Benefits, Interest on Income Taxes Expense	0	(2)
Penalties related to unrecognized tax benefits	$ 0	$ 0