Stock-Based Compensation - Long-Term Stock Award (Details) - Long-term stock awards - $ / shares shares in Millions	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Unvested stock award shares
Balance at the beginning of the period (in shares)	1	1
Vested (in shares)	1	0
Forfeited (in shares)	0	0
Balance at the end of the period (in shares)	0	1
Weighted average grant date fair value
Nonvested, weighted average grant date fair value. beginning of period (in dollars per share)	$ 37	$ 36
Vested (in dollars per share)	37	34
Forfeited (in dollars per share)	37	37
Nonvested, weighted average grant date fair value. end of period (in dollars per share)	$ 38	$ 37