Share-Based Compensation Share-Based Compensation (Performance Share Assumptions) (Details) - $ / shares		3 Months Ended		12 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price	[1]	$ 10.02			$ 29.04		$ 41.97
Expected volatility (b)	[2]	38.30%	34.00%				34.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	[3]	0.40%	2.42%				2.37%
Expected term in years (e)	[4]	3 years	3 years				3 years
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Exercise Price	[5]			$ 0	$ 5.64	$ 9.07
Expected volatility (b)	[6]			0.00%	32.50%	32.50%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	[7]			0.00%	2.50%	2.70%
Expected term in years (e)	[8]			0 years	6 years 6 months	6 years 6 months
Stock options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized for awards (in shares)				0

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

[2] Expected volatility is based on normalized historical volatility of our shares over a preceding period commensurate with the expected term of the performance share units.

[3] he risk-free rate for the expected term of the performance share units is based on the U.S. Treasury yield curve in effect at the time of grant.

[4] For awards subject to service-based vesting, due to the lack of historical exercise and post-vesting termination patterns of the post-Merger employee base, the expected term was estimated using a simplified method for all awards granted in 2020, 2019 and 2018.

[5] The weighted-average fair value was based on stock options granted during the period.

[6] Expected volatility is based on normalized historical volatility of our shares over a preceding period commensurate with the expected term of the option.

[7] e risk-free rate for the expected term of the option is based on the U.S. Treasury yield curve in effect at the time of grant.

[8] For awards subject to service-based vesting, due to the lack of historical exercise and post-vesting termination patterns of the post-Merger employee base, the expected term was estimated using a simplified method for all awards granted in 2020, 2019 and 2018.