Stock-Based Compensation - Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Stock based compensation expense
Total stock-based compensation expense, before income taxes	$ 24	$ 27	$ 32
Income tax benefit	(6)	(7)	(8)
Total stock-based compensation expense, net of income taxes	18	20	24
Unrecognized compensation cost for all stock-based compensation awards	$ 36
Weighted average period for recognition of unrecognized compensation cost for all stock-based compensation awards	1 year 10 months 24 days
Tax benefit from exercise of stock options and other awards	$ 4
Selling, general and administrative expense
Stock based compensation expense
Total stock-based compensation expense, before income taxes	20	23	28
System operations expense
Stock based compensation expense
Total stock-based compensation expense, before income taxes	4	4	4
Long-Term Incentive Plans | Restricted Stock Units
Stock based compensation expense
Total stock-based compensation expense, before income taxes	18	16	21
Long-Term Incentive Plans | Performance Shares
Stock based compensation expense
Total stock-based compensation expense, before income taxes	5	10	10
Non-Employee Directors' Plan
Stock based compensation expense
Total stock-based compensation expense, before income taxes	$ 1	$ 1	$ 1