CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018		Mar. 31, 2017
Cash Flows From Operating Activities:
Net income	$ 208	[1]	$ 351
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation, depletion and amortization	143		106
Amortization of debt issuance costs	2		2
Gain on derivatives, unsettled	(2)		(146)
Stock-based compensation	4		6
Other	3		(1)
Change in assets and liabilities:
Accounts receivable	46		53
Accounts payable	(17)		(13)
Taxes payable	(12)		(8)
Interest payable	(4)		(24)
Other assets and liabilities	(7)		(14)
Net cash provided by operating activities	364		312
Cash Flows From Investing Activities:
Capital investments	(302)		(340)
Proceeds from sale of property and equipment	6		2
Other	2		4
Net cash used in investing activities	(294)		(334)
Cash Flows From Financing Activities:
Payments on current portion of long-term debt			(25)
Change in bank drafts outstanding			6
Preferred stock dividend	(27)
Cash paid for tax withholding	(1)
Net cash used in financing activities	(28)		(19)
Increase (decrease) in cash and cash equivalents	42		(41)
Cash and cash equivalents at beginning of year	916		1,423
Cash and cash equivalents at end of period	$ 958		$ 1,382

[1] In 2018, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.