Stock-based Compensation (Narrative) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($)
Stock Options [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Contractual term	10 years
Years until vest	3 years
Stock options, subject to performance or market-based vesting conditions	None
Unrecognized compensation expense	$ 22
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 4 months 24 days
Retention Awards [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Years until vest	4 years
Unrecognized compensation expense	$ 113
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 10 months 24 days
Performance Retention Awards [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Requisite service period	37 months
Contractual terms of award	We expense two-thirds of the fair value of the units that are probable of being earned based on our forecasted ROIC over the 3-year performance period, and with respect to the third year of the plan, the remaining one-third of the fair value is subject to the relative three-year OIG.
ROIC performance period	3 years
Unrecognized compensation expense	$ 30
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 9 months 18 days