Earnings Per Share Computations (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Basic And Diluted Earnings Per Share Computations And Antidilutive Securities Excluded [Abstract]
Weighted Average Number of Shares Outstanding, Basic	132	131	130
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0	2	2
Weighted Average Number of Shares Outstanding, Diluted	132	133	132
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	3	0	0