Other Financial Statement Data (Details) - USD ($) $ in Millions		7 Months Ended	12 Months Ended
		Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	May. 31, 2013
Receivables
Trade			$ 572.7	$ 624.9
Non-trade			108.2	132.1
Current receivables, gross			680.9	757.0
Less: Allowance for doubtful accounts			5.9	2.6
Current receivables, net			675.0	754.4
Inventories
Raw materials			68.1	114.6
Work in process			435.9	505.1
Finished goods			991.0	1,025.5
Operating materials and supplies			68.5	73.1
Inventory, net			1,563.5	1,718.3
Other current assets
Final price deferred	[1]		175.6	49.9
Income and other taxes receivable			249.4	201.9
Prepaid expenses			123.1	63.8
Other			81.8	52.6
Total other current assets			629.9	368.2
Other Assets
MRO inventory			118.1	115.0
Restricted cash	[2]		851.4	215.2
Other			309.5	224.0
Other Assets, Noncurrent			1,279.0	554.2
Accrued liabilities
Non-income taxes			24.9	29.9
Payroll and employee benefits			162.9	172.8
Asset retirement obligations			91.9	87.9
Customer prepayments			121.2	101.6
Future capital commitment	[3]		120.0	0.0
Other			450.9	333.9
Total accrued liabilities, current			971.8	726.1
Other noncurrent liabilities
Asset retirement obligations			749.7	771.6
Accrued pension and postretirement benefits			69.6	77.6
Unrecognized tax benefits			79.2	89.2
Other			132.1	261.6
Total other noncurrent liabilities			1,030.6	1,200.0
Restricted Cash and Investments, Noncurrent [Abstract]
Restricted Cash Related to Asset Retirement Obligation			630.0
Interest expense, net was comprised of the following:
Interest income		$ 9.5	35.8	21.3	$ 18.8
Less interest expense		22.8	133.6	128.9	0.0
Interest income (expense), net		$ (13.3)	$ (97.8)	$ (107.6)	$ 18.8

[1] Final price deferred is product that has shipped to customers, but the price has not yet been agreed upon. This has not been included in inventory as it is not held for sale.

[2] Included in restricted cash, as of December 31, 2015, is $630 million that is committed to be placed in trust following the effectiveness of the consent decrees discussed under the "EPA RCRA Initiative" in Note 20 of our Notes to Consolidated Financial Statements, as financial assurance to support certain estimated future asset retirement obligations.

[3] Future capital commitment for a non-consolidated company as discussed in Note 8 of our Notes to Consolidated Financial Statements.