Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Cash Flows from Operating Activities
Net earnings including noncontrolling interest	$ 40.1	$ (1.1)
Adjustments to reconcile net earnings including noncontrolling interests to net cash provided by operating activities:
Depreciation, depletion and amortization	217.5	158.8
Noncash or Part Noncash Acquisition, Inventory Acquired	(30.1)	0.0
Deferred and other income taxes	(63.2)	59.1
Equity in net loss (earnings) of nonconsolidated companies, net of dividends	3.3	0.0
Accretion expense for asset retirement obligations	12.1	6.5	$ 25.7
Share-based compensation expense	15.7	15.9
Unrealized gain on derivatives	14.2	1.8
(Gain) loss on sale of fixed assets	0.4	0.0
Other	8.3	9.0
Changes in assets and liabilities, excluding effects of acquisition:
Receivables, net	62.5	45.7
Inventories	(147.6)	(133.3)
Other current and noncurrent assets	(137.5)	(67.7)
Accounts payable and accrued liabilities	(74.9)	38.6
Other noncurrent liabilities	8.2	12.7
Net cash provided by (used in) operating activities	(71.0)	146.0
Cash Flows from Investing Activities
Capital expenditures	(223.3)	(223.8)
Purchases of available-for-sale securities - restricted	(185.7)	(736.1)
Proceeds from sale of available-for-sale securities - restricted	184.0	734.3
Investments in consolidated affiliate	1.3	(25.0)
Proceeds from sale of fixed assets	1.2	0.0
Payments to Acquire Businesses, Gross	(994.6)	0.0
Other	(3.3)	5.0
Net cash used in investing activities	(1,220.4)	(245.6)
Cash Flows from Financing Activities
Payments of short-term debt	0.0	(14.5)
Proceeds from issuance of short-term debt	65.3	143.0
Payments of structured accounts payable arrangements	(235.7)	(35.3)
Proceeds from structured accounts payable arrangements	173.8	107.3
Payments of long-term debt	(206.9)	(1.6)
Proceeds from issuance of long-term debt	0.0	1.3
Cash dividends paid	(9.6)	(96.4)
Other	(0.2)	(1.6)
Net cash provided by (used in) financing activities	(213.3)	102.2
Effect of exchange rate changes on cash	13.4	3.0
Net change in cash, cash equivalents and restricted cash	(1,491.3)	5.6
Cash, cash equivalents and restricted cash-beginning of period	2,194.4	711.4	711.4
Cash, cash equivalents and restricted cash-end of period	703.1	717.0	2,194.4
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	659.4	675.3	2,153.5
Restricted cash in other current assets	9.4	7.1
Restricted cash in other assets	34.3	34.6	32.6
Cash, cash equivalents and restricted cash-end of period	703.1	717.0	$ 2,194.4
Supplemental Disclosure of Cash Flow Information:
Interest (net of amount capitalized)	11.1	8.3
Income taxes (net of refunds)	$ 12.8	$ (0.4)