Long-Term Debt (Interest Rate Swap Narrative) (Details) - Interest rate swap contracts - USD ($) $ in Millions			1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended
	Nov. 05, 2019	Mar. 27, 2019	Nov. 30, 2019	Jun. 30, 2019	Mar. 31, 2019		Dec. 31, 2019		Dec. 31, 2019		Mar. 31, 2020		Dec. 31, 2018
Derivative [Line Items]
Derivative, Term of Contract	7 years
Derivative, Notional Amount	$ 550	$ 650			$ 650		$ 550		$ 550		$ 550		$ 650
Derivative, Average Fixed Interest Rate	1.615%				1.493%	[1]	1.615%	[1]	1.615%	[1]	1.615%	[1]	1.493%	[1]
Derivative, Floor Interest Rate	0.00%
Derivative terminated		441	$ 171	$ 38	$ 441		$ 650
Amount received from terminated interest rate swap		$ 11	$ 0	$ 1	$ 11				$ 12
Interest Rate Swap, Remaining Unamortized Amount											$ 7
Derivative, Fixed Interest Rate	3.365%

[1] Before the application of the applicable borrowing margin.