Share-Based Compensation (Summary of Option Transactions) (Details) - $ / shares		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Mar. 31, 2020	Dec. 31, 2017
Share-based Payment Arrangement [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price	[1]		$ 29.04	$ 10.02	$ 41.97
Stock Option Activity
Number of options outstanding, beginning balance		4,842,400
Number of options granted		0
Number of options exercised		0
Number of options cancelled		(244,000.0)
Number of options outstanding, ending balance		4,598,400	4,842,400
Stock Option Weighted Average Exercise Price
Options outstanding, weighted average exercise price per share, beginning balance (in dollars per share)		$ 29.68
Options granted, weighted average exercise price per share (in dollars per share)		0
Options exercised, weighted average exercise price per share (in dollars per share)		0
Options cancelled, weighted average exercise price per share (in dollars per share)		28.08
Options outstanding, weighted average exercise price per share, ending balance (in dollars per share)		$ 29.77	$ 29.68
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, Weighted average remaining contractual term (in years)		4 years 2 months 12 days	5 years 3 months 18 days
Options exercisable, number of options (in shares)		3,460,800
Options exercisable, weighted average exercise price per share (in dollars per share)		$ 31.47
Options exercisable, Weighted average remaining contractual term (in years)		3 years

[1] The weighted-average fair value was based on performance share units granted during the period.