Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
Cash Flows from Operating Activities
Net earnings including noncontrolling interest	$ (204.0)	$ 129.9
Adjustments to reconcile net (loss) earnings including noncontrolling interests to net cash provided by operating activities:
Depreciation, depletion and amortization	217.8	218.1
Deferred and other income taxes	(107.3)	5.3
Equity in net loss of nonconsolidated companies, net of dividends	20.0	3.6
Accretion expense for asset retirement obligations	17.3	15.3	$ 62.4
Accretion Expense	0.0	0.0
Share-based compensation expense	(10.1)	15.3
Unrealized (gain) loss on derivatives	51.9	(46.9)
Other	10.7	4.4
Changes in assets and liabilities, excluding effects of acquisition:
Receivables, net	14.8	59.0
Inventories	(24.4)	(304.5)
Other current and noncurrent assets	(107.9)	(66.0)
Accounts payable and accrued liabilities	332.7	(186.7)
Other noncurrent liabilities	(21.6)	(22.3)
Net cash provided by operating activities	189.9	(175.5)
Cash Flows from Investing Activities
Capital expenditures	(263.5)	(313.9)
Purchases of available-for-sale securities - restricted	(210.0)	(186.9)
Proceeds from sale of available-for-sale securities - restricted	203.8	182.3
Payments to Acquire Held-to-maturity Securities	(0.7)	(13.0)
Proceeds from Sale of Held-to-maturity Securities	0.8	2.3
Other	(0.1)	0.3
Net cash used in investing activities	(269.7)	(328.9)
Repayments of Other Short-term Debt	132.6	53.7
Proceeds from Other Short-term Debt	1,105.4	206.0
Cash Flows from Financing Activities
Payments of structured accounts payable arrangements	(412.9)	(319.7)
Proceeds from structured accounts payable arrangements	171.6	209.5
Payments of long-term debt	(14.2)	(10.1)
Cash dividends paid	(18.9)	(9.6)
Payments of Ordinary Dividends, Noncontrolling Interest	(0.1)	(0.1)
Net cash used in financing activities	698.3	22.3
Effect of exchange rate changes on cash	(68.9)	13.5
Net change in cash, cash equivalents and restricted cash	549.6	(468.6)
Cash, cash equivalents and restricted cash-beginning of period	532.3	871.0	871.0
Cash, cash equivalents and restricted cash-end of period	1,081.9	402.4	532.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents				$ 1,069.2	$ 519.1	$ 384.6
Restricted cash in other current assets				8.6		8.8
Restricted cash in other assets				4.1	5.4	9.0
Cash, cash equivalents and restricted cash-end of period	1,081.9	402.4	$ 871.0	$ 1,081.9	$ 532.3	$ 402.4
Supplemental Disclosure of Cash Flow Information:
Interest (net of amount capitalized)	15.5	10.5
Income taxes (net of refunds)	$ 66.5	$ 93.8