Stock Transactions And Stock-Based Compensation Stock Transactions And Stock-Based Compensation (Summary of Share Activity) (Details) - shares shares in Millions		12 Months Ended
	Mar. 01, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Preferred stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period		1.7	0.0	0.0
Issuance of stock		1.7	1.7	0.0
Balance, end of period		3.4	1.7	0.0
Common stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period		835.5	817.9	812.5
Issuance of stock	12.1	10.9	12.1	0.0
Common stock-based award activity		4.5	4.6	4.6
Common stock issued in connection with acquisitions		0.0	0.0	0.2
Common stock issued in connection with LYONs’ conversions		0.4	0.9	0.6
Balance, end of period		851.3	835.5	817.9