General Information (Unaudited) (Details) - USD ($) $ in Millions		3 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
General Information [Abstract]
Employee separation charges		$ 34	$ 258
Production and delivery charges		30	202
Depreciation, depletion, and amortization		$ 3	32
Selling, general, and administrative expense			15
Mining exploration and research expense			$ 8
Expected long-term rate of return on plan assets	2.40%			3.40%
Discount rate used in calculating benefit obligation	6.25%	3.25%	3.25%	6.50%
Accumulated benefit obligation, decrease for curtailment during period			$ 184
Increase in plan assets during period			103
Curtailment loss recognized		$ 4
Net funded status of defined benefit plan		$ 888	$ 888