Supplemental Information (Earnings Per Share) (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share Reconciliation [Abstract]
Weighted-average Common Shares Outstanding – Basic	247,000,000.0	245,600,000	243,800,000
Assumed settlement of performance share units and restricted stock units (in shares)	1,200,000	1,400,000	2,000,000.0
Dilutive effect of forward sale agreement (in shares)	500,000	100,000	0
Weighted Average Number of Shares Outstanding, Diluted (in shares)	248,700,000	247,100,000	245,800,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)	0	0	0