Stock-Based Compensation (Unrecognized Compensation Costs) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Share Based Compensation Unrecognized and Non-Vested Cost [Line Items]
Unrecognized Compensation Cost	$ 68
Weighted Average to be Recognized	1 year 2 months 8 days
Stock awards
Share Based Compensation Unrecognized and Non-Vested Cost [Line Items]
Unrecognized Compensation Cost	$ 19
Weighted Average to be Recognized	1 year 7 months 6 days
Performance shares
Share Based Compensation Unrecognized and Non-Vested Cost [Line Items]
Unrecognized Compensation Cost	$ 49
Weighted Average to be Recognized	1 year 14 days