Supplemental Gas and Oil Information (Unaudited) Standardized Measure Of Future Net Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2017	Dec. 31, 2016
Discounted Future Net Cash Flows Relating to Proved Oil and Gas Reserves [Line Items]
Federal income tax rate	21.00%
Future cash inflows	$ 26,482.6	$ 14,447.6	$ 22,028.9
Future production costs	(9,539.9)	(6,070.6)	(9,074.2)
Future development costs	(4,441.5)	(2,275.2)	(4,726.0)
Future income tax expenses	(2,553.6)	(845.8)	(1,439.1)
Future net cash flows	9,947.6	5,256.0	6,789.6
10% annual discount for estimated timing of net cash flows	(4,991.9)	(2,579.7)	(3,692.3)
Standardized measure of discounted future net cash flows	$ 4,955.7	$ 2,676.3	$ 3,097.3	$ 1,928.0